2 small block loaves white bread
80g butter, softened
2 Tbsp Dijon mustard
1½ cups grated cheddar cheese
1 cup grated gruyere cheese
Fine salt, to season
Preheat oven grill to high. Using a bread knife, remove all crusts from loaves. Cut bread lengthways into 12 thin slices. Using a rolling pin, gently flatten slices. Spread with 1/3 of the butter and mustard. Combine cheeses in a bowl and sprinkle over bread. Starting at 1 short end, roll up bread, enclosing cheese. Spread rolls with another 1/3 of the butter.
Put rolls on an oven tray and put under grill. Cook for 5 minutes, turn over, then cook for a further 5 minutes or until toasted on all sides. Spread with remaining butter, season with salt and serve.