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.
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.
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.