Grilled Cheese Sandwich

In a bowl, combine the cheeses and mix until blended. Set aside.

On a large work surface, lay out the bread slices and spread them evenly with the butter. Then turn them buttered-side down on the surface and spread the other side thinly with the mustard.

Sprinkle half of the cheese mixture evenly onto the mustard-spread side of 4 of the slices. Lay 2 tomato slices atop each cheese-topped slice and then sprinkle the remaining cheese evenly over the tomatoes. Top the sandwiches with the remaining 4 slices of bread, mustard side down, and press down gently to compact the sandwiches.

Heat a large nonstick frying pan or griddle to medium heat. Working in batches if necessary and using a spatula, carefully transfer the sandwiches to the hot pan or griddle. Cook, pressing down gently on each sandwich with the spatula 3 or 4 times, until golden and slightly crusty on the first side, 3-4 minutes. Carefully turn over the sandwiches and continue cooking, again pressing down on them, until the second side is golden and the cheese has begun to ooze out the sides slightly, 2-3 minutes longer.

Transfer to individual plates and serve immediately.