Mix together schmaltz, stock, truffle oil, salt, and eggs. Thoroughly mix in matzo meal. Refrigerate for 1 hour. Form into golf balls and stuff with a teaspoon of shiitake gribenes in the center, and cook, covered, in 2 quarts of boiling chicken stock for 20 minutes until light as a feather but also heavy as a cannon ball.
You may substitute duck or goose schmaltz (not ortelon schmaltz, it's too bony) You can use a little more salt, but it's not good for you.
Saute chicken skin until fat exudes and lightly golden. Saute onion until deep golden brown. Add garlic and saute for 2 minutes. Strain to separate solids from oil and reserve both. Saute mushrooms in 1 tablespoon of the oil in the pan until wilted.
Remove shiitakes and reserve for the matzoh balls. Nosh on the gribenes, shmeared on rye bread.