Preheat the oven to 350 degrees F. Lightly butter a nonstick mini cheesecake pan.
Sift the flour, baking powder and salt in a medium bowl and set aside.
In a large mixing bowl, cream the butter and sugar for 4-5 minutes. Add the vanilla extract. Add the eggs, one at a time, beating after each until incorporated. Using a rubber spatula, fold the flour mixture into the wet mixture until incorporated. Be careful not to over-stir or the cakes will be dense.
Spoon the batter into the mini cheesecake cups to the halfway point. Bake on the middle oven rack for 12-15 minutes or until a toothpick inserted into the center of a cake comes out clean.
Allow the cakes to sit in the cupcake pan for a couple of minutes before transferring them to a wire rack to cool completely.
To make the buttercream filling, beat together the butter, powdered sugar and milk until smooth. If the buttercream is too stiff, add a tiny amount of milk until a spreadable consistency is reached. If it's too runny, add more powdered sugar. Spoon the buttercream into a piping bag with a medium or large round tip.
Once the cakes have cooled completely, slice them in half.
Pipe a dot in the center of the bottom cake half and pipe 4-5 more dots around the center dot. Spoon some jam on top, carefully helping it to run between the dots for a prettier presentation.
Place the top cake half in position and repeat for the remaining cakes. Sift powdered sugar over the top of the cakes. Store the cakes in an airtight container.