Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking dish or line it with parchment paper.
Mix the dry ingredients: In a medium-sized bowl, whisk together the flour, baking powder, and baking soda. Set this mixture aside.
Cream the wet ingredients: In a large bowl, beat together the brown sugar, peanut butter, and butter until smooth and creamy. Add the eggs one at a time, mixing well after each addition. Stir in the milk.
Combine: Gradually fold the dry ingredients into the wet mixture, stirring just until combined. Be careful not to overmix—this keeps the cakes fresh and fluffy.
Bake: Pour the batter into your prepared baking dish and spread it out evenly. Bake for 20–25 minutes, or until a toothpick inserted in the centre comes out clean.
Make the frosting: While the cakes are cooling, prepare the frosting. In a medium bowl, mix the powdered sugar with milk or cream until smooth. Adjust the consistency by adding more powdered sugar if it’s too runny.
Frost the cakes: Once the snack cakes are completely cool, spread the frosting evenly on top. Sprinkle chopped peanuts over the frosting for added crunch and flavour.
Serve: Slice into squares and enjoy! These peanut butter cakes are perfect for an afternoon pick-me-up or as a quick treat for your family and friends.