Preheat oven to 350F.

Cook pasta in boiling water as normal until just past firm.

In a separate bowl, mix together white sauce, mushrooms, tuna, salt, pepper and asparagus.

Drain water from pasta and add to mixture. Stir together.

Pour into a buttered casserole dish.

Add shredded cheese to top.

Bake at 350F for 25-30 minutes.

Add optional crunchy topping for last 5 minutes of baking, if desired.

In a small, heavy saucepan, melt 2 tablespoons of butter over low heat.

Blend 2 tablespoons of flour into the melted butter.

Add 1/4 teaspoon of salt.

Cook over low heat, stirring, for 4 to 5 minutes. Cooking for this length of time will minimize 'flour' taste.

Slowly add 1 cup of milk, stirring constantly.

Continue cooking slowly until smooth and thickened.