*Whisk the eggs together in a small bowl and weigh them. Adjust if needed: remove some of the egg mixture to get 165g exactly.
Method
Preheat oven to 390°F (200°C). Grease a 9×5-inch (22x12-cm) loaf pan with butter and dust with flour.
Using a spatula or a whisk, cream butter and sugar together until light and fluffy. Add in the eggs and mix until well incorporated.
In a separate bowl, sift together the flour, baking powder, baking soda and salt. Combine with the wet ingredients, and mix until just incorporated. Add in the 60g of milk, and mix until just incorporated.
Divide the batter in two separate bowls. In the first bowl, stir in the vanilla extract. In the second bowl, stir in the cocoa powder with one tablespoon of milk.
Using a large spoon, dollop about 1/3 of a cup of the vanilla batter into the prepared pan and spread it evenly along the bottom. Using another large spoon, dollop the same amount of chocolate batter in the middle, and spread it out (pushing it down slightly in the middle and leaving some of the vanilla cake mix visible all around the edges).
Repeat with a layer of vanilla cake mix, and then a layer of chocolate cake mix (always pushing the batter slightly in the middle, and leaving some of the batter underneath visible around the edges – to create that wavy marbled pattern when sliced). Repeat, alternating the layers, until all the batter is used. To create marbling, run a sharp knife through the batter in a swirling motion.
Bake for 10 minutes. Lower the heat to 350°F (180°C) and bake for 40 minutes, until a cake tester comes out clean.
Transfer to a cooling rack, and let cool at least 15 minutes before slicing.
This cake is delicious warm or cool. You can keep it for up to three days on your kitchen counter, well wrapped in a tin or foil.
Slice the cake to enjoy the swirling marble effectgrafvision/Shutterstock
Audrey Le Goff is a French food writer, photographer, and creator of the food blog Pardon Your French, where she shares recipes and stories from her beloved home country, France. She is the author of the cookbook “Rustic French Cooking Made Easy” (2019). She currently lives in Brittany. Follow her on Instagram @pardonyourfrench