Leftover Meat Pie

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