Instructions:
- Combine the three types of shredded cheese and a pinch of black pepper in a bowl.
- Spread a thin, even layer of softened butter right to the edges on only one side of each of the four bread slices. This will be the exterior.
- Flip two slices of bread butter-side down onto a clean surface. Optionally, spread a very thin layer of Dijon mustard on the unbuttered side of these two slices. Divide the mixed cheese evenly and layer it generously onto the mustard/bread.
- Top with the remaining two slices of bread, ensuring the buttered sides are facing up.
- Place the assembled sandwiches into a large non-stick skillet or cast-iron pan that is currently cold or barely warm. Turn the heat on to LOW to MEDIUM-LOW. Cooking slowly is crucial.
- Cook slowly for 5–6 minutes until the bottom side is a deep, uniform golden brown. If it browns too fast, turn the heat down further.
- Gently flip the sandwiches. Press down very lightly with a spatula to ensure full contact. Cook for another 5–6 minutes until the second side is golden and the cheese is fully melted.
- Immediately remove the sandwiches from the pan. Let them rest on a cutting board for 1 minute before slicing diagonally. Serve hot.