Chocolate Buckwheat Cake

Name: Chocolate-Buckwheat Cake
Ingredients: 6 ounces (170g) bittersweet or semisweet chocolate (chopped); 1/2 cup (115g) unsalted butter (cubed); 4 large eggs (separated); 1/2 cup (100g) unrefined or granulated sugar; 1/3 cup (80ml) plain whole-milk yogurt; 1 teaspoon vanilla extract; 1/2 teaspoon salt; 3/4 cup (75g) almond or hazelnut flour ((see Note below)); 1/4 cup (35g) buckwheat flour