Preheat your oven to 180°C (350°F). Grease and flour a cake pan to ensure your cake comes out perfectly.
In a large mixing bowl, beat the eggs and sugar together until the mixture is light and fluffy. This should take about 5-7 minutes.
Sift the flour, salt, and baking powder together, then gently fold it into the egg mixture until just combined.
Pour the batter into the prepared pan, smoothing the top with a spatula. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
While the cake bakes, prepare the buttercream! In a separate bowl, beat the softened butter until creamy. Gradually add powdered sugar and cocoa powder, mixing until smooth.
Once combined, mix in the orange marmalade and orange liqueur into the buttercream until evenly incorporated.
Once the cake is thoroughly cooled, frost it generously with the chocolate buttercream.
For an extra touch, drizzle more orange marmalade on top or add chocolate shavings for decoration.
Slice, serve, and enjoy!