1. Preheat the oven to 390°F (200°C). Line a muffin tin with 12 paper liners and set aside. Melt the chocolate for the dough and set aside too cool down.

 

2. Add the butter, sugar, and vanilla extract to a large bowl and mix until light and fluffy. Add the eggs one after another and mix in well after each addition. Add the melted and cooled chocolate and mix in. Mix the flour with cocoa, baking powder and salt in a smaller bowl and then add together with the milk to the large bowl and mix until just combined. Fill the batter into the prepared paper liners and bake for 16-18 minutes or until a toothpick inserted into the center comes out clean. Take out of the oven and let cool down completely.

 

3. Chop the chocolate for the chocolate sauce and add together with the sugar, butter, and heavy cream to a microwave-safe bowl. Heat up in several intervals in the microwave until the chocolate has melted and you can mix everything to get a smooth sauce. You can also do that in a bowl over a pot with simmering water. Set aside to cool down a bit.

 

4. For the buttercream add the room temperature (!) butter to a large bowl and mix on high speed for about 5 minutes until very light and fluffy. Sift the cocoa into the bowl and mix in. Add the vanilla extract and salt and mix in as well. While still mixing gradually add the sweetened condensed milk – do this very slowly or the buttercream might curdle. Continue mixing until you get a nice and fluffy buttercream. Fill into a piping bag with a star tip and set aside.

 

5. Core the cupcakes with a cupcake corer or a sharp knife to get some space in the center of each cupcake. Fill the holes with chocolate sauce and pipe a good amount of buttercream on top. If you still have some chocolate sauce left you can use that to decorate the cupcakes as well.