re: Medieval farmers ate 7000-9000 calories a dsy

Forget the butter. It would be too labor intensive. Think about the seasonal milk production and not letting it go to waste...make cheese and store it for late fall and winter usage.
Now let's butcher an old animal with fatty tissues: first you are going to eat the organ meats. Then the tough muscles go into stews (crack the bones and enjoy the marrow). All that fat isn't going to waste. If you are wealthy, some of it might be made into soap. Most will go into use as food, sopped up by bread (not all bread was wheat based. Regionally other grains were more productive and dependable.
The grains that were used for beer and other alcoholic drinks, after the alcohol happened, the leftovers became animal feed or sorts of heavy 'breads'.

If you ever go to Louisberg on the Atlantic coast of Nova Scotia, (like Williamsburg but French and fewer tourists), they sell a hard tack bread that is close to what their settlers ate. But if the baker is in a chatty mood he'll tell you that the real thing was so hard most people couldn't bite into it much less chew it. It would have been edible dunked in a stew.