Preheat your oven to 350°F (175°C) and line a muffin pan with paper liners.

In a bowl, cream room-temperature butter and granulated sugar until light and fluffy.

Beat in the eggs one at a time until fully incorporated.

Sift together flour and baking powder over the batter and gently fold in.

Pour in vanilla extract and stir until evenly distributed.

Fill muffin liners two-thirds full with batter.

Bake for 10 to 12 minutes until golden and a toothpick comes out clean.

Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Slice each cake in half, spread jam on the bottom, add buttercream, and replace the top.