Leftover Meat Pie - cooking recipe

Ingredients

mashed potatoes (instant works well, for 4 people)
1 large onion, cut in 1-inch pieces
1/4 c. butter or margarine
1/4 c. flour
1 1/2 c. warm milk
2 bouillon cubes
1/2 tsp. salt
1/4 tsp. pepper
1/4 tsp. celery salt
2 c. cooked meat, cut into 1-inch pieces
1 can peas and carrots
1 can mushrooms

Preparation

Brown onion in butter.
Add flour, stock and seasonings.
Cook until thick, then simmer about 5 minutes.
Add meat and vegetables.