01 -
Heat the oven to 175°C / 350°F. Line a 23 × 13 cm loaf pan. Whisk flour, baking powder and salt together.
02 -
Beat butter and sugar until pale and fluffy, about three minutes. Beat in eggs one at a time, then vanilla.
03 -
Fold in the flour mixture in two additions, alternating with 70 ml milk. Divide the batter equally between two bowls.
04 -
Mix peanut butter into one half. Whisk cocoa with the remaining 30 ml milk to a smooth paste and fold into the other half. Both batters should be thick but spoonable.
05 -
Alternate spoonfuls of the two batters in the prepared pan. Draw a skewer through in two or three long curves, without fully blending the colors. Level the top gently.
06 -
Bake for 50–55 minutes until a skewer inserted in the middle comes out without wet batter. Cool in the pan for 15 minutes, then on a rack for at least 30 minutes more before slicing.
07 -
Keep fully cooled loaf airtight for up to three days at cool room temperature, or freeze individual slices. No icing or additional topping is required.