Melt the butter in a saucepan over a low heat. Cut the crusts off the bread slices, and, using a pastry brush, spread 6 or 7 on both sides with melted butter (reserving some for the rest).
Brush melted butter on the other slices of bread and press them on top. Sprinkle on the remaining sugar and add any melted butter that's left over.
Bake the pudding for 50-55 minutes or until the top is crisp, golden and crunchy and the apples inside are soft.
Pre-heat the oven to gas mark 4, 350F (180C).