Note: Parts of this post comes from an earlier post of mine where I explained viking diet.

Generally, the Scandnavian people of the era had a bit better access to food compared to their continental brethren. This was mostly because Scandinavia was less densely populated, which meant there were room for cash crops (or other ventures intended to produce something to trade, such as sheep rearing for wool, charcoaling, tar cooking and so on) and that a relatively large portion of the Scandinavian peasants owned their own land. In the late medieval period, Swedish self-owning peasants owned about 52% of the arable land, and they and their households made up about 62% of the population.

Swedes especially had access to wild game (both large and small through hunting), sea fowl eggs and both fresh and sea water fish. Compared to many continental peasants, the Scandinavians ate more proteins and slightly more dairy.

Meat and fish was dried, smoked or salted (the latter most common, at least towards the end of the medieval era) to last during the long winter months. Salt came from Frisia and later from the salt mines around Lüneburg in northwestern Germany and the Hansaetic League dominated the trade.

Pork was considered the finest meat, but wild game (moose, venison, hares and boar), beef, mutton and goat was also eaten. Herring and cod were the most common fish eaten, but bass, pike, salmon, trout and whitefish were also common. Dried cod was frequently imported from Norway and eaten during lent, while salted herring was consumed both locally and exported.

Cereal was common, but not as dominating as further south. Wheat was rare - barley, oats and rye were the most common ones, baked into dark bread or hard Swedish crisp style bread, boiled into porridge or mixed with milk to make gruel. One of the more common ways to preserve cereal was to brew it into a weak (1-2% ABV) and cloudy dark beer that was drunk by everyone, including children.

Milk from goats were common, cow milk was rarer. Dairy was mostly used in cooking, or to make sourcream, yoghurt, cheese or salted butter.

Vegetables such as turnips and white and red cabbage were common staple food. Peas, beans, radishes, carrots, yellow onions, leek, celery and kale were also common.

Spices were rare but not unheard of, local grown spices, such as horseradish, mustard seeds, angelica, garlic, dill, thyme, cummin, fennel, lovage and sweet gale were used extensively while exotic spices such as cardamom, cinnamon and pepper were luxuries eaten by the wealthy.

Fruits were eaten as available and in season - mostly apples, but also pears. Nuts, such as hazelnut and walnut was not uncommon either.

Honey was pretty much the only sweetener and a luxury.

Weak beer was the most common drink (after water, of course). Milk was mostly used in cooking, but sometimes drunk. Strong beer, imported wine and mead (made from honey) were luxuries.

It was common to eat two large meals a day (perhaps with snacks or small meals in between).

Porridge or gruel, perhaps with a patch of butter or some animal fat or tallow, a piece of bread (often hard, Swedish crispbread style) with butter and cheese could be a sensible breakfast.

The most common way of cooking was boiling, and the many well-made large iron pots from the era bear witness of this. As meat was often salted to last, boiling it with other ingredients was a common way to reduce the saltiness. A meat and vegetable soup, perhaps with some freshly baked soft bread could be a common dinner. The traditional Swedish peasoup (a dish of boiled dried yellow peas, yellow onions and salted and smoked pork) probably has its roots in this era.

Dipping your bread in the stock leftover from boiling meat (especially pork) was considered a treat, and is still something done at christmas. It was also a common snack or quick bite inbetween meals - dried or salted meat needed a long time to boil, and dipping a piece of bread in the hot stock and eating it whiel the meat was boiling was a common way of getting something hot and decently filling quickly while waiting for support.

Common dishes include peasoup, fried porridge with animal fat or small pieces of meat, boiled turnips with butter and saucage. For regular people, large pieces of meat would most likely only be eaten during festivals and feasts, such as christmas or right before lent.

Food was eaten out of large wooden bowls - people did not have their own plates, with knife and spoon. Forks had not yet made their entrance.

To summarize:

1. What sort of dishes did the commoners eat?

Boiled dishes with little meat. Peas, beans, dark bread, weak beer, turnips, tallow and butter spiced with locally grown spices.

2. What sort of the dishes did the nobles/royalties eat?

Rich meat dishes from animals specifically raised for their meat (unlike the peasants). Dishes including exotic spices. Pork was considered one of the finest meats since it was always raised for meat only. Wine, strong beer and honey (or mead made from honey) would be luxuries enjoyed by the upper clases.

3. Was the food mostly bland or did they have a variety of spices to use?

Not bland. It could be increadibly salty, though. Salted herring could be almost inedible. Local herbs and spices were used.

4. What were some of the techniques used to cook their food?

Boiling, mostly.

5. Are there any books that I can find which talks about making medieval food?

I don't have any singular source, I am afraid.

To begin, a disclaimer-- I'm not exactly an expert on this. I know this particular subreddit prefers actual, professional historians, but I did read a book called "A Time Traveler's Guide to Medieval England" (by Ian Mortimer, who is actually a professional) that contains substantial chapters on food. It's an awesome book, and if you're looking for more information on the subject of daily life in the 14th century or so, that'll probably have the answer.

As for now, I'll tell you what I remember:

1. Usually bread. I'm talking about western Europe and England here, but the norm would be black bread. When you talk about commoners I'm assuming you mean relatively poor rural Yeomen and "villeins" (serfs, basically). The "Villeins" would subsist on a wee plot of land reserved for their personal use; they'd farm this when not working on their Master's land. If you were a free man who either owned land or was just renting property, you'd probably still live on the same diet, with perhaps a little more variety, because bread is cheap, and meat is oftentimes reserved for the rich. If you lived in a Royal Forest (and this is by no means exclusive to actual, Robin Hood-style forests, by the way), hunting for any purposes was considered poaching, and, I believe, punishable by death.

2. To put it simply, meat. The richness and variety often of course depended on the wealth of the Household: the King would have a much better meal than a knight poor enough to be relatively indistinguishable from the peasantry. Meat and fish were considered the actual "dishes" of the rich. Everything else, meaning plant-derived substances, was considered "sauce" for the meat. This doesn't mean the rich didn't eat their veggies, it just means said veggies usually came in a heavily modified form. You wouldn't roast broccoli, for instance, and eat it for the sake of eating roasted broccoli; you'd do something to said vegetable and put it with meat. Usually meat dishes were particularly rich, and served as the main course in a feast, in which the noble would dine with his guests, retainers, men-at-arms, household (meaning family, friends, higher-ranking servants, etc.), and particularly less-than-smelly dependents.

3. Here down I'm afraid to say my knowledge is quite a lot more vague. Spices I know were precious material. Commoners would experience a lot more bland of a diet than the rich, because most spices had to be imported from India. Salt came from Africa, and had to be shipped across the Sahara by Camel. When you think about the fact that the whole motivation of the 15th century Portuguese expeditions to find a way around Africa was to establish a sea route to cut the Ottomans out of the spice trade, you can consider the price of spices. Whether this made most food bland is beyond my knowledge, but I can say, at least speculatively, that it might help to picture Corned Beef and Cabbage in it's most tasteless form. (And for the record I love corned beef and cabbage...)

4. Good question. I know local Lords would have large bread ovens they'd use to supply their household and sell surplus at market, and their dependents could use this, but beyond that, I don't know. I'd imagine most cooking would take place over an open fire in some fashion. You'd probably get a lot of roasted meat on spits, but now you're just delving into my imagination.

5. Like I said, most of what I told you above comes from "A Time Traveler's Guide to Medieval England" by Ian Mortimer. It's not specifically about food, per se, but it is an absolutely excellent survey of daily life in the fourteenth century, containing many, many pages devoted to food.

Hope this Helps!

-Severian the Torturer