Ingredients
Method
1.Preheat oven to 200C. Heat oil in a pan. Cook onion 4 to 5 minutes. Add mince and celery and cook 5 to 8 minutes. Add flour and cook 1 minute until mixture thickens. Stir in tomatoes and 1/2 cup boiling water. Bring to the boil, stir in stock cube and season to taste. Simmer 2 to 3 minutes. Remove from heat and stir in pasta. Tip into a gratin dish.
2.To make topping, melt butter in a pan and add flour. Cook 1 to 2 minutes to form a thick paste. Add milk slowly, beating well until mixture comes to the boil. Remove from heat. Add mustard and half the cheese. Season to taste. Spoon sauce over pasta. Sprinkle over remaining cheese. Bake 30 to 40 minutes.