Preheat oven to 350F and grease a 9-inch springform pan very well. Line the bottom with parchment paper.

In a small saucepan over low heat, melt the chocolate until smooth. Set aside to cool.

In a large bowl, beat butter until smooth. Beat in powdered sweetener for several minutes until well combined and smooth. Beat in egg yolks, one at a time, scraping down sides of bowl and beaters as needed. Add chocolate and vanilla extract and beat until well combined.

In another large bowl, beat the egg whites until frothy. Add granulated sweetener and beat on high until soft peaks form. Stir about one quarter of the whites into the chocolate mixture to lighten it, then fold in the remaining whites until almost combined but not quite.

Add almond flour and fold in until just combined. Spread batter in prepared pan and bake 30 to 40 minutes, or until set and a tester inserted in the center comes out clean. Remove and let cool completely.

Run a sharp knife around the edges of the pan to loosen and then remove pan sides. Flip cake out onto a wire rack and carefully cut into two horizontal layers. Carefully transfer one layer to a serving platter (use two large flipping spatulas to help you move the layer without cracking).

In a small bowl, whisk together the apricot jam and water until well combined. Spread about 2/3 of the filling over the first layer of cake. Carefully top with the second layer of cake and spread with remaining filling. Refrigerate while preparing the glaze.

In a small saucepan over medium heat, whisk together whipping cream and powdered sweetener. Bring to just a simmer, then remove from heat and add chopped chocolate and vanilla. Let sit 5 minutes to melt and then whisk until smooth. Let cool 10 minutes to thicken.

Pour glaze over the top of the cake, spreading to the edges. Let it drip slowly down the sides, spreading all over to cover completely.

Refrigerate until glaze is set, about 1 hour. To cut into slices, warm a sharp knife in hot water. Serve with whipped cream (in Austria and Germany, they serve it with unsweetened whipped cream, but you can sweeten yours if you like. I love the creaminess of the unsweetened whipped cream).