Preheat the oven to 180°C.

Line the Le Creuset 18,5cm Mini Loaf Tin with baking paper.

Melt the butter and set it aside. Using an electric mixer, beat the sugar and eggs together until doubled in size and pale in colour. Whisk together the melted, cooled butter, buttermilk and vanilla paste. Slowly add the buttermilk mixture to the eggs and sugar, whisking while you add.

Sift together the flour, baking powder, bicarbonate of soda and salt. Fold the dry ingredients in batches, one-third at a time, into the wet ingredients until just combined. Divide the batter into two separate bowls.

Sift the cocoa powder into one bowl of the batter and gently whisk to combine, making a chocolate batter. Pour alternating batters into the loaf tin to create a marble effect, starting with vanilla, topping with chocolate and then repeating.

Insert a knife into the batter and create a zigzag movement. Bake for 35-40 minutes until a skewer comes out clean. Cool in the tin for 20 minutes before unmoulding and allow to rest on a cooling rack before slicing.