mushroom layer
Night before:
1) Grind 2 lbs mushrooms finely--place in cheesecloth--squeeze out liquid
2) chop onions finely-3/4 cup-saute lightly
3) add mushrooms - cook one minute
4)Add 1/4 cup finely chopped parsley - cook one minute.
5)Take off stove--add sherry and salt to taste. Return to cheesecloth, place in colander inside baking pan. Refrigerate overnight. Squeeze out liquid in morning (be tough--squeeze as much as possible).

beef
Morning of party:
1) cook filet of beef 30-35 mins. at 400 degrees
2) Let cool - save drippings for gravy, discard fat
3) Refrigerate

pastry
Any time after beef is thoroughly cooled:
1) 2-3 large containers of Pillsbury Crescent Dough (two should be enough, but 2 1/2 is safer)
2) work hard at dough with rolling pin (It's very elastic, and you'll be exhausted before you're through). Not paper-thin, but should be fairly thin--too thin and it tears, too thick and it's soggy.
3)Roll out to size of beef, with 1" overlap.

This is the only tricky part--if you want to be really safe, have extra mushroom pate and crescent dough ready in casae you have problems the first time (i.e., my hands got shaky!)
Basically, try to handle pastry/mushroom./beef combination as little as possible--it only causes problems.

1) Put half of pate on top half of beef - cut rolled-out dough in half, put on top of pate.
2) Have ungreased baking pan ready--flip beef onto pan so that uncovered half of beef is up. Put other half of pate on, then other half of dough, then pinch overlapping ends together hard. If pastry is too thin, this is where it will stretch and tear; if not pinched hard enough, it will part. (Doesn't hurt the taste, but the looks will suffer.) Make seams as invisible as possible.
3) Brush with beaten egg
4) Prick all over with a fork.

[this can all be done early in the day--then just refrigerate it until dinner time]

Cook at 375 degrees for 35 minutes. This only cooks the pastry--the meat cooks no longer after it's covered with pastry, amazingly enough. This timing gives you quite pink beef, which is (technically) correct.

gravy
served hot beside beef:
Pan drippings, sherry to taste, a little consomme (depending on how much gravy you want).

Good Luck!!!!!!