Position the oven rack in the center and preheat to 325°F / 165°C.

Butter and grease 2 round 4-inch x 2-inch (10 cm x 6 cm) springform cake pans.

In a separate large bowl, beat the butter and sugar until light and fluffy (about 4–5 minutes). Add the eggs one at a time, beating well after each addition, then add the milk and mix.

Fold in the sifted flour mixture and melted chocolate until smooth and well combined.

Divide the batter evenly between the two pans. The easiest way to ensure even layers is by placing each pan on scales and adding the batter until they weigh the same.

Bake for 40–50 minutes (depending on your oven) or until a toothpick inserted in the center comes out clean.

Allow cakes to cool in the pans for 10 minutes, then transfer to a wire cooling rack and cool completely.

Cream the butter and powdered sugar with a hand or stand mixer until light and fluffy.

Gradually mix in the melted chocolate and cocoa powder, scraping the sides of the bowl to incorporate. If the frosting is too thick, add a little milk. Set aside for 1 hour to firm up.

Two-Tone Red Frosting:
Divide the frosting between two bowls. Add red food coloring to one bowl until you reach the desired shade.
Place both the red and white frosting into a single piping bag to create a swirl effect when piping.