This Chocolate Hazelnut Marble Cake is rich and moist with lovely swirls of chocolate and hazelnut batters. Marble cakes may look complicated, but they actually start with a white batter. Once the batter is made, it is divided in half and then each batch is flavored. The marbling is created by placing the hazelnut and chocolate batters alternately in a baking loaf pan.

Heat oven to 400°F / 200°C. Grease a 10x5x2.5 inch loaf pan, and line the bottom with greaseproof paper.

In a large bowl, beat the butter and sugar together, then add the eggs, one at a time, mixing well after each addition. Fold in the flour and yeast until the mixture is smooth.
Divide the mixture between two bowls. Stir the cocoa powder into the mixture in one of the bowls. Stir the hazelnut powder in the second bowl. Take two spoons, and use them to dollop the chocolate and hazelnut cake mixes into the tin alternately. When all the mixture has been used up, tap the bottom on your work surface to ensure that there aren't any air bubbles. Take a skewer and swirl it around the mixture in the tin a few times to create a marbled effect.

Bake the cake for 45-55 minutes until a skewer inserted into the center comes out clean. When cooked, turn out onto a cooling rack and leave to cool. Will keep for three days in an airtight container, or can be frozen for up to three months.