Ingredients: - 
2 cups macaroni elbows, cooked
2 Tbsp butter
1 onion, finely chopped
2 Tbsp flour
½ tsp Dijon mustard
2 ½ cups Milk, heated
salt and pepper
2 cups freshly grated cheese, gruyere best
2 Tbsp dry breadcrumbs  
METHOD: - 
Preheat oven to 180°C.
Cook the macaroni in a large saucepan of boiling water following packet directions or until al dente.
Drain, return pasta to pot, add butter and toss until melted. Set aside to cool while making the Sauce
Melt the butter in a saucepan, add the onion and cook gently for about 10 minutes or until the onion is translucent.
Stir in the flour and cook, stirring, until frothy. Then add the mustard.
Remove from the heat and add the hot milk gradually, stirring until lump free.
Return to the heat and cook, still stirring, until the sauce boils and thickens. Remove from the heat, season with salt and pepper and add half the grated cheese, and the macaroni.
Combine well and put into an ovenproof dish.
Mix the breadcrumbs into the remaining grated cheese and sprinkle over the top.
Cook for 20 minutes or until golden and heated through.