Step 1

Preheat the oven to 400°F (200°C), with the convection option on, if you have it. Place a baking sheet in the oven to preheat.

Step 2

Spread the butter on one side of each slice of bread, divvying it up evenly among the slices. Place the slices, buttered-side down, on a clean cutting board. Spread the Dijon mustard on top of one slice, then top with the Havarti, turkey, arugula, bacon, and Cheddar. Spread the stone-ground mustard on the second slice of bread, then layer with the Colby Jack, tomato slices, pickle chips, and ham. Place the Swiss on the third slice and arrange the pickled onions and jalapeño on top.

Step 3

Remove the hot baking sheet from the oven and, using a wide spatula, very carefully move the 3 stacks of topped bread to the baking sheet, buttered side down. Bake until the cheeses start to melt and the fillings are warmed through, 3 to 4 minutes.

Step 4

Meanwhile, when you put the baking sheet in the oven, immediately begin to preheat a cast-iron or nonstick skillet over medium-low heat.

Step 5

Using a wide spatula, move the 3 stacks of topped bread to the hot skillet, still buttered side down. Cook until the bottoms are nicely browned, about 2 minutes. Move to a clean cutting board.

Step 6

Very carefully place the Swiss-jalapeño stack of bread, bread side down, on top of the piece with turkey and bacon, then carefully turn over the Colby Jack–ham piece and place it, bread side up, on top of the sandwich. Cut the sandwich into quarters and serve immediately.