Add the chocolate mixture to the egg and creme fraiche mixture and blend them together. Add flour mixture a little bit at a time and beat on low speed until combined. Divide batter equally among the pans.
Make salted caramel buttercream by whipping butter in a bowl of a stand mixer until light and fluffy and then adding prepared caramel or dulce de leche with a pinch of flaky salt until completely incorporated.
Meanwhile, make a chocolate ganache. Bring heavy cream to a boil and take it off the heat immediately, then add your chopped chocolate into it and stir until melted! Cool it and whip it with an electric mixer until paler in colour and fluffy.
For the cake
For the salted caramel buttercream
For chocolate ganache