Slice the brioche buns in half horizontally. Lightly spread 1/2 tbs softened butter on the cut side of each top and bottom half (reserve remaining butter for grilling). Set aside.

Tonijnvulling (tuna filling)

Drain canned tuna well and flake with a fork into a medium mixing bowl.

Add 4 tbs mayonnaise, 2 tbs Greek yogurt, 1 tsp Dijon mustard and 1 tbs fresh lemon juice to the tuna. Stir to combine.

Fold in finely diced red onion (1/4 cup), diced celery (1/4 cup), 1 tsp chopped capers, and 1 tbsp chopped parsley. Mix until evenly distributed.

Season with 1/2 tsp salt and 1/4 tsp black pepper. Taste and adjust seasoning (add a little more lemon or mayo if needed). Cover and chill briefly for 10 minutes to let flavors meld, or proceed immediately.

Cheddar & Jalapeño

Preheat a cast-iron skillet or nonstick pan over medium heat. Grate about 200 g sharp cheddar and have 1 sliced jalapeño ready.

Assemble the sandwiches: spread approximately 3-4 tbs of the tuna mixture over the bottom half of each brioche bun (divide evenly among 4 buns). Top the tuna with an even layer of grated cheddar (about 50 g per sandwich) and arrange a few thin jalapeño slices on top of the cheese to taste.

Finish & garnish

Brush the outside cut sides of each bun (both top and bottom) with the remaining softened/melted butter (about 1/2 to 1 tbs per sandwich total).

Place sandwiches in the preheated skillet. Cook on medium heat for 3–4 minutes, covered with a lid or a sheet of foil to help the cheese melt, until the bottom is golden brown. Carefully flip each sandwich and cook the other side 2–3 minutes until golden and cheese is fully melted. If necessary, reduce heat to low and cover for an additional 1–2 minutes to ensure thorough melting without burning the bread.

Remove from pan. If desired, add sliced pickles or a small piece of lettuce on the bottom half before serving. Serve warm.