Place chopped dark chocolate and butter in a heatproof bowl set over a small saucepan of barely simmering water (double boiler) ensuring the bowl doesn’t touch the water. Stir gently until smooth and glossy, about 3–5 minutes. Alternatively, microwave in 20-second bursts, stirring between bursts, until melted.

Coat molds

Using a pastry brush or small spoon, coat the inside of six 3–4 oz silicone or metal ramekin molds with a thin layer of melted chocolate, covering sides and base. Chill the molds in the refrigerator for 5 minutes to set the first layer.

Second coat

Apply a second chocolate layer to ensure sturdy cups (pay extra attention to the rim). Return molds to the refrigerator until fully set, about 10–15 minutes. If any thin spots appear, add a third thin coat and chill again.

Unmold and dust

Once set, carefully invert molds and remove chocolate shells. If desired, dust the inside lightly with cocoa powder (tap out excess). Set shells aside on a tray. Keep refrigerated until filling is ready.

Espresso Pot de Crème

Preheat and prepare

Preheat oven to 300°F (150°C). Bring a kettle of water to a boil for the water bath.

Warm milk and cream

In a medium saucepan, combine whole milk and heavy cream and warm over medium heat until just steaming and small bubbles form around the edges (do not boil), about 4–6 minutes. Remove from heat.

Dissolve espresso

Stir the 1 tablespoon brewed espresso into the hot milk/cream. If using espresso powder, dissolve it in a teaspoon of hot milk before adding to ensure even distribution.

Whisk yolks and sugars

In a medium bowl, whisk together the egg yolks, granulated sugar, and brown sugar until smooth and slightly pale, about 1–2 minutes.

Temper eggs

Slowly pour about one-third of the hot milk mixture into the yolk mixture while whisking constantly to temper the yolks. Then gradually whisk in the remaining milk mixture until fully combined.

Add flavorings

Stir in the vanilla extract and a pinch of salt. If you want a stronger espresso flavor, add the optional 1 teaspoon espresso powder and whisk until dissolved.

Strain custard

Strain the custard through a fine-mesh sieve into a clean bowl or measuring cup to remove any coagulated bits for a silky texture.

Fill chocolate cups

Place the unmolded chocolate shells in a shallow baking dish. Pour the strained custard into the chocolate cups, filling each to about 1/8 inch from the rim (reserve any extra custard).

Bake in water bath

Place the baking dish with filled cups in the oven. Carefully pour the hot water into the baking dish to come halfway up the sides of the cups to create a bain-marie. Bake at 300°F (150°C) until custards are set but still slightly wobbly in the center, about 25–30 minutes. Time will vary with cup size—check at 20 minutes.

Cool

Remove the baking dish from the oven and carefully lift cups out of the water bath. Let cups cool to room temperature on a wire rack, then refrigerate until thoroughly chilled and firm, at least 2 hours or up to overnight.

Garnish and Serve

Finish and garnish

Before serving, optionally pipe or spoon a dollop of whipped cream onto each pot de crème. Sprinkle with chocolate shavings and top with an espresso bean or cocoa nib. If desired, warm the chocolate cup rim for 3–5 seconds with a blowtorch or warm spoon and press a small extra chocolate shard for a decorative rim.

Serve

Serve chilled. Each filled chocolate cup yields one portion.