Preheat the oven to 350°F and grease a 12-cup muffin tin, or line with paper liners.

Whisk the flour and baking powder together in a small bowl and set aside.

Beat the butter and sugar together until pale and fluffy, about 3 minutes with a hand mixer.

Add the eggs one at a time, beating well after each, then mix in the vanilla.

Fold in the flour mixture in two additions, stirring just until no dry streaks remain.

Divide the batter evenly among the muffin cups, filling each about two-thirds full.

Bake for 16 to 18 minutes, until the tops spring back when pressed lightly and a toothpick comes out clean.

Cool the sponges in the tin for 5 minutes, then turn out onto a wire rack to cool completely, about 30 minutes.

Once cool, slice each sponge in half horizontally with a serrated knife.

Spread a teaspoon of jam over the bottom half of each sponge.

Pipe or spoon a swirl of whipped cream over the jam, then replace the top half, pressing down very lightly so the filling just peeks out at the sides.

Dust with powdered sugar just before serving, so it does not melt into the cream while the sponges wait.