Bring the butter to the right temperature: place 2 tablespoons unsalted butter in a small skillet over medium heat. Melt the butter and continue cooking until it foams and turns a deep golden-brown with nutty aroma (about 2–3 minutes). Watch closely and swirl the pan — this 'browned butter' adds a caramelized, nutty backbone that complements the peanut butter. Remove from heat immediately and transfer to a heatproof bowl so residual heat doesn't burn it.

Prepare the spreads (why order matters): If using vanilla and/or lemon zest, stir 1/4 tsp vanilla and 1/4 tsp lemon zest into the peanut butter in a small bowl — this lifts the peanut flavor and balances the jam's sweetness. Warm the peanut butter for 10–15 seconds in the microwave or stir vigorously so it spreads easily; spreadability prevents tearing the bread and encourages even coverage, which forms a moisture barrier.

Assemble the sandwiches: Lay out four slices of bread. Spread 2 tablespoons peanut butter evenly on two slices (the peanut butter should form a solid layer that will keep the jam from soaking into the bread). On the remaining two slices, spread 1 tablespoon jam each. Close the sandwiches with the jam face down onto the peanut-buttered slice. Press gently to bond the layers — this helps the sandwich hold together when grilling.

Brush the browned butter on the outsides: Using a pastry brush or spoon, lightly brush the browned butter across the outside faces of each sandwich (about 1/2 Tbsp per outer face). Brushing rather than slathering gives controlled browning and prevents greasiness while still delivering that deep, caramelized flavor. If your browned butter has solids, whisk them back in briefly so the fat distributes smoothly.

Pan-fry to golden perfection: Heat a heavy skillet or nonstick pan over medium-low heat. Place a sandwich in the pan and press gently with a spatula or a second pan to create even contact; cook 2.5–3 minutes per side until the bread is deep golden and crisp and the filling warms through. Cooking low and steady develops an even crust without burning the butter — too-high heat will char the outside before the interior warms.

Rest briefly and finish: Transfer sandwiches to a cutting board and let them rest 1 minute; this relaxes the filling and keeps the jam from spilling out when you slice. If using flaky sea salt, sprinkle a tiny pinch over the cut sandwich to enhance contrast and make the flavors pop.

Slice and serve: Cut each sandwich diagonally (classic presentation) and serve immediately while warm and gooey. Pair with a crisp side (apple slices or kettle chips) to balance richness.