Preheat oven to 175C and set aside a large casserole dish. In alarge bowl, mix crushed crackers with 30g of butter and set aside.
Melt the rest of the butter in a large saucepan over medium heat.Add ham and fry till ham is lightly browned. Gradually add flour in,mixing well before slowly whisking milk in. Add salt, mustard, cayenneand season well with freshly ground black pepper, mixing well.
Add 2 cups of cheese in and keep stirring till cheese is melted.Turn heat off and stir macaroni in. Transfer mixture to the casseroledish and top with crackers mixture. Bake for 20 minutes. Serves 8