Potato-Patch Casserole

Ingredients

• 1 lb. ground beef
• 1/2 c. chopped onion
• 1/4 c. milk
• 1/4 c. dry bread crumbs
• 1 tsp. salt
• 1/4 tsp. pepper
• 1/4 tsp. celery salt
• oil
• egg
• 1 Tbsp. margarine
• 2 Tbsp. flour
• 1 c. milk
• 1 1/4 tsp. salt
• dash of pepper
• 1/2 lb. Velveeta cheese
• 4 c. potato slices
• 1 (10 oz.) pkg. frozen peas and carrots, thawed (canned peas and carrots can be substituted)