Combine cheeses, milk and cornstarch in a bowl and refrigerate, for 2 hours.
When ready to make the fondue: Set up a fondue pot, double boiler, or place a bowl over a saucepan of simmering water. Melt the butter in the pan or bowl. Then add the cheese mixture and heat gently, stirring until the cheese has melted and the mixture is thick enough to coat the back of spoon. Take care to regulate the heat to make sure the water doesn't boil, as overheating the cheese will cause it to curdle. Add the apple brandy just before serving. Keep warm and serve with the selection of dippers.