Squash Casserole

4 C. yellow summer squash, thinly sliced and cooked
1 C. finely chopped onion
2 Tbsp. butter
1/2 C. mayonnaise
1/2 C. sour cream
2 eggs, slightly beaten
2 tsp. sugar
2 tsp. salt
pepper to taste
1 C. grated Swiss cheese

Topping:
1 C. crushed butter crackers
1 stick butter, melted
1 C. chopped pecans

Saute onion in 2 Tbsp. butter. Mix all ingredients  and pour into a greased  9 X 9 in. casserole dish. Stir together cracker crumbs and butter and spread over casserole. Bake at 350 degrees F 30 min. Sprinkle nuts over top and cook 5-10 more min. or until nuts are toasted.