Preheat the oven to 275 degrees. Grease and line a 9-inch round cake or spring form pan with parchment paper.
Cream the butter, margarine, or coconut oil in the bowl of a standing mixer with the paddle attachment. Add the sugar and mix until fluffy.
Add the egg yolks, 1 at a time, mixing well after each addition.
Melt the chocolate with the liqueur in a double boiler, then cool slightly and stir in the vanilla. Add the chocolate to the butter-sugar mixture and blend well.
Sift the cake flour or potato starch with the salt, then stir into the chocolate mixture.
Beat the egg whites until stiff but not dry in the standing mixer with the whisk attachment. You know the whites are done if you can hold the bowl upside down and the whites do not fall out. Fold the whites gently into the chocolate mixture until just incorporated.
Pour the batter into the prepared pan and bake for 35 to 45 minutes or until a toothpick inserted in the center comes out clean.
Cool the cake for a few minutes in the pan. Put three pieces of parchment paper on a serving platter so each piece overlaps the other slightly in the middle. When the cake is slightly cooled but still warm, slide a knife around the edges of the cake to loosen the sides from the pan. Flip the cake onto the prepared serving platter, so the bottom is now the top.
The Toppings: Apricot jam and chocolate glaze
To make apricot glaze: Combine the apricots, 1 cup of the sugar, lemon zest, and 1 1/2 cups of water in a saucepan set over medium-high heat. Bring to a simmer, lower the heat, and cook, stirring occasionally, until the apricots soften and absorb most of the water, about 30 minutes. Stir more constantly at the end of cooking to avoid scorching. Puree the mixture in a food processor. This will yield 2 cups. Store in an airtight container in the refrigerator for up to 1 week or freeze for up to 6 months.
To make the chocolate glaze: Combine the chocolate with the 1/2 cup of sugar and 1/2 cup of water in a saucepan set over low heat, stirring constantly until the chocolate melts and the glaze thickens slightly, about 10 minutes.
Now, top your cake: Spread 1 cup of the apricot jam on the top of the cake with a metal cake spatula. Then pour the chocolate glaze evenly over the cake, spreading the glaze onto the sides. Carefully remove parchment paper. Allow to cool completely before serving. Serve alone or with a dollop of schlag (whipped cream).