Chocolate Ganache (prepare the day before)

1. Place the chopped chocolate in a heatproof bowl.
2. Heat half of the heavy cream until just simmering.
3. Pour the hot cream over the chocolate and let sit briefly, then stir until smooth.
4. Add the remaining cold cream and mix until fully incorporated.
5. Blend with an immersion blender until smooth, cover with plastic wrap touching the surface, and chill for 4–6 hours (overnight if possible).

Marble Cupcakes

1. Bake in a preheated 180°C (350°F) oven and line a cupcake pan with paper liners.
2. In a bowl, sift together the dry ingredients: flour, baking powder, baking soda, and salt.
3. In a large bowl, cream the butter and sugar for 2–3 minutes until light.
4. Add the eggs and vanilla and mix again until smooth.
5. Fold in the dry ingredients and buttermilk alternately until just combined.
6. Divide the batter in half and mix the cocoa powder into one portion.
7. Spoon dollops of both batters into the liners and swirl gently with a knife or toothpick.
8. Bake for about 18 minutes, until set and lightly golden.
9. Let cool briefly, then transfer to a wire rack to cool completely.

Assembly

1. Whip the chilled ganache on medium speed for about 1 minute until creamy and firm.
2. Transfer to a piping bag fitted with a decorative tip and pipe swirls onto the cupcakes.
3. Sprinkle with chocolate shavings if desired and refrigerate for 1 hour before serving.