Preheat the oven to 350°F (175°C) and grease and line a 9-inch round cake pan with parchment paper.

1. Cream together the butter and sugar until light and fluffy. Add egg yolks one at a time, beating well after each addition. Stir in vanilla extract.
2. Sift together flour, baking powder, cocoa powder, and salt. Gradually fold into the butter mixture until just combined.
3. Beat the egg whites until stiff peaks form and gently fold them into the batter in three additions. Fold in the melted dark chocolate.
4. Pour the batter into the prepared pan and bake for 30-35 minutes or until a toothpick comes out clean. Let it cool for 10 minutes before transferring to a wire rack to cool completely.
5. Slice the cake horizontally into two layers. Heat apricot jam until liquid and smooth, then spread over the bottom layer before placing the top layer back on.
6. To make the glaze, heat heavy cream over medium heat. Add the chopped dark chocolate and let it sit for 1-2 minutes, then stir until smooth. Add butter and stir until glossy.
7. Pour the glaze over the cake, smoothing it over the top and sides. Let it set for 1 hour or refrigerate for 15-20 minutes to set faster.
8. Serve with whipped cream if desired and enjoy!