Preheat your oven to 375°F. Grease an 8-inch round baking pan thoroughly, covering the bottom and all the way up the sides.

Trace the bottom of the pan onto parchment paper, cutting the circle slightly larger than the pan itself. Line the bottom of the pan with this parchment circle.

Melt the butter in a small saucepan over low heat. Once melted, add the chocolate chips and stir continuously as they begin to soften.

When the chips are about halfway melted, remove the pot from the heat and keep stirring until smooth and glossy.

Alternatively, place the butter and chocolate chips in a microwave-safe bowl and heat at half power in 30-second bursts, stirring after each round.

Transfer the melted chocolate mixture into an electric mixer bowl. Add sugar and vanilla extract, then mix for a few seconds until combined.

Beat in the eggs one at a time, letting each fully incorporate before adding the next.

Add cocoa powder, baking powder, and salt. If using, add espresso powder now. Mix until just incorporated.

Spread the batter into the prepared pan and sprinkle coarse sea salt on top.

Bake for 25-30 minutes depending on your texture preference.

Let the cake cool to room temperature in the pan before removing it.

Finely chop the baking chocolate and place it in a heatproof bowl.

Heat the cream until scalding hot but not boiling. Pour over chopped chocolate and let it sit for a minute, then stir until smooth.