Marble Pound Cake

Ingredients: 150 g unsalted soft butter 1 1/2 cups sugar (300 g) 1 tsp vanilla extract 4 large eggs 3/4 cup milk 2 cups all purpose flour (300 g) 2 tsp baking powder pinch of salt 4 tbsp unsweetened cocoa powder to add on half of the batter - Bake at 350 F/180 C for about 50-55 minutes or until a skewer inserted in the center comes out clean.