Preheat the oven to 325°F. Butter and flour a 9-inch springform pan.
Melt the chocolate in a double boiler or microwave; set aside.
Beat the sugar and butter in a large bowl with a mixer until creamy.
Add the egg yolks one at a time, blending after each addition. Add the vanilla.
Fold in the chocolate and flour.
In a separate bowl, beat the egg whites until stiff peaks form. Fold them into the batter.
Pour the batter into the prepared pan and bake for 50 to 60 minutes, until a knife inserted in the center comes out clean. Let cool in the pan for at least 1 hour.
To make the apricot glaze, heat the apricot preserve with the lemon juice for few seconds in the microwave.
Once completely cooled, using a long serrated knife, trim the top of the cake to level it. Cut the cake horizontally into two equal layers.
Place the bottom layer in a cake stand. Brush the top of the cake layer with the apricot glaze.
Place the second cake layer on top and brush again. Brush the top and sides of the cake with the remaining glaze. Let cool for about 10 minutes in open air.
Make the chocolate ganache
Melt the butter in a double boiler over medium-high heat. Add the chocolate and corn syrup and cook, stirring constantly, until the chocolate is melted. Remove from the heat, stir in the vanilla.
Pour all of the warm chocolate ganache on top of the cake.
Using an offset spatula, gently smooth the ganache over the cake, allowing it to run down the sides.
Refrigerate until the ganache is completely set, at least 1 hour. Remove the cake from the refrigerator about 1 hour before serving.