Venison Stroganoff

1 lb fresh mushrooms
3/4 cup butter, divided
1 1/2 lb venison, cubed
2 tbsp flour
2 cups beef bouillon
1 tsp dry mustard
2 cups pale dry sherry
1 lg onion, sliced
2/3 cup sour cream

Saute mushrooms in 1/4 cup butter until tender.  Set aside.  Add at least 1 tbsp
butter to pan.  Add venison and brown.  Set aside.  If little butter remains, add
2 tbsp butter and sprinkle in 2 tbsp flour.  Combine all ingredients except sour
cream.  Simmer on low for 25 minutes.  About 5 minutes before serving, add
sour cream and blend well.