Place 85 g butter and 100 g dark chocolate in a heatproof bowl set over a saucepan of gently simmering water (double boiler) or in short bursts in the microwave (20–30 sec, stir between). Stir until completely melted and smooth. Remove from heat and allow to cool for 3–5 minutes.

Mix sugars and egg

In a separate bowl, whisk together 100 g granulated sugar and 25 g light brown sugar. Add 1 large egg and 1 tsp vanilla extract, whisking until glossy and slightly thickened (about 1 minute).

Combine chocolate and egg mixture

Slowly pour the slightly cooled chocolate-butter mixture into the egg-sugar mixture while whisking continuously to temper the egg and produce a smooth batter.

Dry ingredients

Sift together 60 g all-purpose flour, 15 g unsweetened cocoa powder, and 1 tsp fine sea salt (and 1 tsp espresso powder if using). Fold the dry ingredients into the chocolate mixture with a spatula until just combined — do not overmix.

Portion and bake

Spoon or pipe batter into the prepared mini muffin cups, filling each about two-thirds full (approximately 1 heaping tablespoon each). Tap the pan once on the counter to remove air bubbles. Bake at 170°C (340°F) for 10–13 minutes for fudgy centers (edges set, centers slightly jiggly). For cakier bites, add 1–2 minutes.

Cool

Remove pan from oven and let brownie bites cool in the pan for 5 minutes, then transfer to a wire rack to cool completely (about 20–30 minutes). Keep the mini cups intact if using liners.

Belgian Chocolate Sauce

Warm the cream: In a small saucepan, heat 120 ml heavy cream with 1 tablespoon light corn syrup over medium heat until it just begins to simmer at the edges (do not boil).

Combine with chocolate: Place 120 g finely chopped Belgian dark chocolate in a heatproof bowl. Pour the hot cream over the chocolate and let sit for 1 minute to soften, then whisk gently from the center outward until smooth and glossy.

Finish sauce: Add 10 g room-temperature butter and a pinch of sea salt. Whisk until shiny and fully incorporated. If sauce is too thick, thin with up to 1–2 tsp warm water or additional warm cream. Keep warm over very low heat or in a thermos until serving; stir occasionally.

Finishing & Service

Assemble: Arrange cooled brownie bites on a serving platter. Spoon or drizzle warm Belgian chocolate sauce over each brownie bite just before serving (about 1 tsp sauce per bite).

Garnish: Lightly sprinkle crushed freeze-dried raspberries over the sauced brownie bites so they cling to the chocolate. Add a light dusting of unsweetened cocoa powder or powdered sugar if desired, and finish each with a tiny pinch (a few flakes) of coarse sea salt for contrast.

Serve: Serve immediately while the sauce is slightly warm and the centers are fudgy. Leftover brownie bites can be stored in an airtight container at room temperature for up to 2 days (store sauce separately in the refrigerator for up to 5 days; gently rewarm).