Start by allowing the bread to reach room temperature before assembling the sandwich. Spread softened butter on the outside of each bread slice so it grills into a golden crust. This step creates the classic crispy texture that makes the melt special.
Mix whole grain mustard, mayonnaise, honey, and olive oil in a small bowl until smooth. Spread this mixture on the inside of the bread slices to add creaminess and a sweet-tangy flavor. The spread helps bring all the ingredients together.
Place prosciutto, salami, and pepperoni evenly over half of the bread slices. Add red onion, roasted red pepper, and cornichons for freshness and texture. Try to distribute the fillings evenly so every bite feels balanced.
Sprinkle mozzarella and provolone over the meat layers. Add fresh rosemary and thyme along with a little black pepper. The cheese should cover the fillings well so it melts into every layer during grilling.
Close the sandwiches with the remaining bread slices, keeping the buttered sides facing outward. Heat a grill pan over medium heat and cook each sandwich for about 3 to 4 minutes until the bread becomes golden and the cheese begins melting.
Carefully turn the sandwiches over using a spatula. Grill the second side until crispy and the cheese is fully melted. Avoid very high heat because the bread can brown too quickly before the cheese melts.
Remove the sandwiches from the pan and let them rest for 1 to 2 minutes. This allows the melted cheese to settle and keeps the filling from spilling when sliced. Cut into halves and serve warm.