6tbspespresso or 2 tbsp espresso powder steeped with 1/4c boiling water
1tspvanilla extract
1chazelnut mealalmond meal works too
1tspsalt
1csugardivided
4eggsseparated
Instructions
Preheat your oven to 350 F. Butter a 9-inch springform pan then place it on top of a baking tray.
Place the chocolate into a medium sized mixing bowl. Melt the butter, vanilla and espresso in a saucepan over medium-low heat. As soon as the the mixture starts to simmer, pour it over the chocolate. Let sit for 1-2 minutes then stir with a whisk until is smooth.
In a separate large mixing bowl whisk together the egg yolks and 1/2c sugar. Whisk until the mixture becomes thick and pale then fold in the hazelnut meal and salt followed by the melted chocolate mixture.
In a stand mixer (or hand held mixer) beat the egg whites and remaining 1/2c of sugar on high until glossy stiff peaks form about 5 minutes. Gently fold the whipped egg whites into the chocolate-hazelnut mixture with a rubber spatula. Transfer the batter to the prepared pan and bake until puffed slightly and set along edges but still slightly wobbly in center, 35 to 40 minutes.
Let cool completely then slide a paring knife along the sides of the cake pan to release any bits that may be stuck then release the sides. Slice and serve with warm espresso!
Notes
Hazelnut flour can be hard to find (and expensive!) feel free to substitute almond flour instead.