Pierogi Fillings, Meat

Yield:	12 Servings
Categories:	Pasta, Polish

1 1/2	lb	Ground beef or ground beef and pork
2	lg	Onions (finely chopped)
1/2	lb	Butter, divided
		Salt and Pepper to taste
1	c	Chopped mushrooms (optional
4	tb	Sour cream (optional)