Instructions

• Preheat the oven to 350°F (175°C).
• Butter and flour an 8×8-inch cake pan and set it aside.
• In the bowl of an electric mixer, cream 3 tablespoons softened butter and 1/4 cup peanut butter together until smooth and combined.
• Add 1/3 cup brown sugar and beat until the mixture is light and fluffy.
• Add 1 egg and 1 teaspoon vanilla extract and beat until fully incorporated.
• With the mixer on low speed, add 1 cup whole wheat pastry flour (or all-purpose flour), 1 teaspoon baking powder, and 1/4 teaspoon salt. Mix until the dry ingredients are just combined, scraping down the sides of the bowl occasionally.
• Add 1/2 cup milk and mix on low until the batter comes together and is smooth; avoid overmixing.
• Pour the batter into the prepared 8×8-inch pan and smooth the top with a spatula.
• Drop spoonfuls of jelly or jam of your choice over the top of the batter (add as little or as much as you like).
• Use a knife to gently swirl the jelly into the batter to create a marbled pattern.
• Bake at 350°F for 20–25 minutes, or until the cake is set and a toothpick inserted in the center comes out with a few moist crumbs (not wet batter).
• Remove the cake from the oven and let it cool completely in the pan before slicing and serving.