Prepare the bread pockets: If your slices are thin, trim crusts and pair up to make 4 sandwiches (2 slices per serving). Press 50 g chopped dark chocolate into the center of each sandwich (about a generous tablespoon per sandwich) so the chocolate is enclosed. This creates a molten center that will stay contained during dipping and searing.

Make the custard: In a large shallow bowl or pie plate whisk together 4 large eggs, 240 ml whole milk, 120 ml heavy cream, 25 g granulated sugar, 1 tsp vanilla, 1/2 tsp cinnamon and 1/4 tsp fine sea salt. Whisk until smooth and slightly frothy. The eggs set the structure while the milk/cream balance richness (cream = silkiness, milk prevents it from becoming too heavy).

Rest the sandwiches briefly: Place the chocolate-stuffed sandwiches on a sheet tray and refrigerate 10 minutes. Chilling firms the bread and chocolate slightly so the sandwich holds together while you dip and sear; it also helps prevent the chocolate from leaking immediately into the pan.

Dip the sandwiches: Heat a large heavy skillet over medium heat and add 1 tablespoon of butter (reserve the rest). Quickly dip one sandwich at a time into the custard for 8–10 seconds per side, pressing lightly so custard soaks into the bread but doesn't collapse the sandwich. You want the center saturated but not soggy—the exterior should form a custard crust when seared.

Sear to golden perfection: Add 1 tablespoon butter to the hot skillet and set the dipped sandwich in. Cook 3–4 minutes per side over medium (adjust to medium-low if browning too fast), adding another tablespoon of butter as needed. The goal is a deep golden crust that contrasts with the soft interior; searing at moderate heat develops the Maillard flavor without burning the sugar in the custard.

Finish in the oven if needed: If the crust is browning before the center is warm and chocolate is melting, transfer the skillet (ovenproof) to a 175°C/350°F oven for 3–5 minutes to gently finish. This ensures the chocolate becomes lusciously molten without over-browning the outside.

Make the quick vanilla-caramel drizzle: While the last sandwiches cook, make a simple caramel in a small heavy saucepan—combine 50 g (¼ cup) granulated sugar and 2 tbsp water over medium heat without stirring (tilt pan to encourage even melting). Once the sugar turns an amber color, remove from heat and whisk in 30 g (2 tbsp) cold unsalted butter and 60 ml (1/4 cup) warm heavy cream little by little (stand back as it will bubble). Stir in a pinch of salt and 1/2 tsp vanilla. This creates a glossy, slightly salted sauce that brightens chocolate and adds complexity. (If you prefer, skip the caramel and use warmed maple syrup or a dusting of powdered sugar.)

Plate with care: Trim any burnt edges, cut each sandwich diagonally, place two halves per plate, spoon warm vanilla-caramel over them and dust with powdered sugar and optional orange zest. The diagonal cut exposes the molten chocolate for a dramatic restaurant presentation.

Serve immediately: French toast is best right away when the contrast between hot, melting chocolate and crisp crust is at its peak. If left too long the crust will soften and the chocolate will set.