Preheat oven to 275 degrees. Butter a 9-inch round springform pan.
Place butter and chocolate in a large glass bowl and heat in the microwave for 30-second increments, stirring each time until combined and smooth. If you do not have a microwave, you can soften the butter and chocolate by placing a mixing bowl over a pot of water simmering over low heat. Be careful though the bowl may get hot.
Once softened enough to combine, add espresso, salt, and egg yolks to the chocolate and butter mixture; stir until combined.
Using a large bowl with a whisk or a stand mixer on medium-high, beat egg whites until fluffy soft peaks form.
Slowly add sugar and continue to beat until glossy and stiff peaks form.
Gently fold in the egg whites into the chocolate mixture, one-half at a time, until combined.
Pour into the prepared pan and bake for 45 to 50 minutes or until cooked through and a toothpick inserted into the center comes out clean.
Allow to cool 5 minutes in the pan then run a knife around the edges and carefully remove the pan.
Dust with confectioner’s sugar, slice and serve.
Nutrition information shown is an estimate and is not to be assumed to be accurate. If accurate information is required for your diet or lifestyle, please calculate the nutrition yourself using a tool you trust.
Recipe from 730 Sage Street Flourless Chocolate Cake https://www.730sagestreet.com/flourless-chocolate-cake/