In a small bowl combine 1 tablespoon mayonnaise and 1 teaspoon sour cream. Finely chop the 2 tablespoons pickled jalapeños and add to the bowl along with 1 teaspoon pickling liquid (or lime juice), 1 teaspoon garlic powder, 1 teaspoon ground black pepper, and 1/4 teaspoon salt. Stir until smooth and well combined. Taste and adjust heat or salt as desired. Set aside.

Assemble Sandwiches

Prepare croissants

Using a sharp serrated knife, carefully slice each croissant horizontally about two-thirds through so the top remains attached (or slice completely in half if preferred).

Spread and layer

Generously spread about 1/2 tablespoon of the jalapeño mayonnaise on the bottom half of each croissant and a light smear (about 1/4 teaspoon) on the top half. On the bottom half layer 2 slices of deli ham, then 1 slice of sharp cheddar and 1 slice of pepper jack (you can overlap the cheese slices). If you like extra heat, add a few thin slices from the optional fresh jalapeño on top of the cheese. If using cilantro, scatter about 1/2 tablespoon over the cheese layer.

Close and press

Close each croissant gently. Press down slightly to compact the sandwich so the fillings hold together.

Toast / Finish

Pan-toast method

Heat a nonstick skillet or cast-iron pan over medium-low heat. Add 1/2 tablespoon of the unsalted butter and allow it to melt and coat the pan. Place 2 sandwiches in the pan (work in batches if needed), buttered-side down. Lightly butter the exposed top of each croissant with the remaining butter. Cook for 2–3 minutes until the bottom is golden and the cheese begins to melt, then carefully flip and cook another 1.5–2 minutes until the other side is golden and the cheese is fully melted. Reduce heat if the croissant browns too quickly.

Oven method (alternate)

Preheat the oven to 350°F (175°C). Place assembled croissants on a baking sheet lined with parchment. Lightly brush the tops with melted butter. Bake for 8–10 minutes until the croissants are warmed through and cheese is melted. For a crisper top, broil 30–60 seconds while watching closely.

Serve

Remove sandwiches from pan or oven. Let rest 1 minute, then slice in half if desired. Serve immediately with extra jalapeño mayonnaise on the side for dipping.