Preheat oven to 325°F (160°C). Grease a 9-inch (24cm) round springform pan and line the bottom with parchment paper.

Grind the almonds in a food processor until fine. Mix the instant espresso powder into the ground almonds.

In a clean, dry bowl, whip the egg whites until stiff peaks form. Gently fold in the powdered sugar and the almond-espresso mixture until just combined.

Pour the batter into the prepared pan and bake for 35-40 minutes until the top is firm and slightly golden. Let the cake cool completely in the pan.

For the cream, combine egg yolks, heavy cream, granulated sugar, and vanilla in a small saucepan.

Cook over medium-low heat, stirring constantly with a whisk or spatula, until the mixture thickens enough to coat the back of a spoon. Do not let it boil.

Remove the custard from heat and let it cool to room temperature. It is crucial that the custard and butter are the same temperature before mixing.

Whisk the soft, cubed butter into the cooled custard a little at a time until the mixture is smooth, thick, and yellow.

Spread the cream evenly over the cooled almond base while it is still in the pan or after moving to a serving platter.

Melt the dark chocolate and drizzle it over the cream in a decorative pattern, then sprinkle with flaky sea salt.

Refrigerate for at least 1 hour to allow the cream to set before slicing.