Rich and chocolaty, this gluten-free cake has all the flavor and none of the guilt. Top this cake with powdered sugar, fresh berries, whipped cream, or enjoy on its own.
Heat oven to 300°F. Line a 9 x 13” cake pan with parchment paper and spray generously with cooking spray.
Melt chocolate chunks and butter in a double boiler over gently simmering water. Stir continuously until the mixture is smooth. Once melted, reduce to low heat.
Separate egg yolks and egg whites into two bowls. In the bowl with egg yolks, add in half the sugar (1/3 cup), instant coffee, and vanilla extract. Beat at high speed until pale and combined. Slowly stir in melted chocolate and continue beating at low speed until just incorporated. Set aside.
Use an electric mixer at medium speed to whisk the egg whites until frothy. Gradually add remaining sugar (1/3 cup) and mix until firm (but not dry) peaks form.
Fold half of the chocolate mixture into the egg whites until just incorporated. Repeat folding the remaining chocolate mixture into the egg whites being careful not to overstir.
Pour batter into the cake pan and bake for 35 – 40 minutes until the cake has risen in the center. Allow cake to cool inside the pan for at least 20 minutes before icing, slicing, and enjoying.