What did the richest medieval lords eat each night?

Set aside the wild world of splendors for all and a 19th-20th century conception of "the gentry versus the help." The demonstration and reinforcement of strict social hierarchy was indeed a chief goal of later medieval everyday dining practices in elite households--but its structure looked and functioned somewhat differently than we might imagine.

Most importantly, there was no principle of equality in offered food. People were served--were permitted--different amounts and especially different types of food based on their rank in the lord's or king's household. In 1318, for example, royal ordinances from Edward II's court show that clerks with a rank of esquire or above were allowed the portion of ale, wine, bread, the major roasted course, and another meat course; while those with a rank of valet or below (assistants to the above, for example) could not enjoy the roast dish. From the esquires ascending to courtiers and the royals themselves, larger portions and sometimes more courses would be on offer.

Second, our distinction between "diner" and "servant" would be blurred. This applied especially not to 'public' meals, but to the private, separate meals that kings/lords and queens/ladies would take in their own residences. It was a great honor among ladies-in-waiting to be invited to dine with the queen or duchess, and that honor included being the one to serve her meal! Of course there were actual servants as well; it's just, the idea of a very highly placed noblewoman as a serving lady is not something we'd usually think of, so I wanted to mention it upfront.

Who got to dine with or near the lord and lady was a central question of medieval hierarchical etiquette, but barely scratched the surface of what went into orchestrating the social aspects of an elite medieval meal. It was good manners to start a meal off with the collective call to wash one's hands and face. "Cup and ewer" or basin sets, often gilt or fancy in some other way, adorned the table and would be used at appropriate moments. Far from "out of sight, out of mind," these sets were key heirlooms and treasured gifts. It seems that some people had their own; others were shared, although it's not entirely clear to me from the description. Towards during-meal cleanliness, places would also be set with individual cleaning cloths; I'm not sure why so many scholars have an objection to saying napkins, but...basically napkins. It was imperative that they, like tablecloths, be of high-quality fabric, often linen.

Other pre-meal rituals included ones you might be more familiar with than hand-washing at the table: blessing the food and blessing the people in attendance. (Preacher John Mirk also suggested thanking God after the meal was over.)

Medieval dining tables, hauled into place for a meal, would be covered with a tablecloth. Sometimes there would be additional cover-cloths laid over the first. This was because medieval plates--trenchers--were not always plates. In addition to the ubiquitous street-food technique of "bake everything into a pastry crust for easy transport," medieval food service often meant scooping the course onto a crusty, even stale piece of bread. In such a case, an over-tablecloth was by etiquette standards mandatory. However, some elite families had reuseable trenchers (perhaps with a bread trencher on top). These could be made out of fancy metal or an ordinary one, or even wood. And make no mistake, people were well aware of the monetary as well as social value of gold and silver trenchers, as well as goblets. Servants in the household of the archbishops of Canterbury in the 14th century made it a habit to search the bags of departing guests at the gates to make sure that drinking and dining vessels had not mysteriously jumped into their luggage!

Back in the hall: Illuminations often show extra bread-trenchers stacked on the table along with actual bread to be eaten. Ideally, there would be more than one meat course at a given meal. Note that time of year--Lent! fast days!--could switch things up tremendously. Of course, by the fifteenth century, socially ascendant nobles and urban gentry with money to burn could buy their way out of fasting obligations--the purgatorial version of a carbon emissions offset fee, one imagines.

Courses were sometimes brought as an individual dish to a specific person; other times, a communal pot would be shared by two people picking out the food onto their own trenchers. Sauces may have been served separately, in bowls to be scooped out of with a spoon. Knives and spoons were the utensils of choice; there was plenty of lip-smacking, finger-licking eating with their hands going on. Yes, even in polite company!

In addition to the serving dishes and eating vessels, tabletops would be adorned with several other standard items. One was what we might compare to centerpieces: some kind of display, often based around something that had started life as edible but was decorative in this purpose. Another was an amulet popularly known as a "serpent's tongue." These were either believed or superstitiously accepted to zap any poison out of food! The little ritual was to touch one's food or dish to the serpents' tongue before consuming it, which would neuter any poison. My suspicion is that for some people, this was believed to be truly effective; for others, it was a mindless little "lucky socks" kind of superstition. Note that these could be shaped like many things that were not a serpent's tongue, such as palm branches. Finally, there were elaborate decorative items in statement shapes, like the king's heraldry done in gold or a sapphire-encrusted swan.

I've talked more about the actual types of food that would be present elsewhere in this thread. I hope this helps fill in some of the surrounding details for what it would have been like to attend a lavish yet ordinary meal at court in the late medieval West.