In a large bowl, beat butter with sugar until fluffy; beat in egg and vanilla.
In a separate bowl, whisk together flour, baking powder and salt; stir into the butter mixture in 3 additions.
Wrap dough in cling wrap and put it in the fridge for 30-60 min to cool, so it is easier to rollout.
Between sheets of waxed paper, roll out dough to 1/8-inch (3 mm) thickness. With a 21/2-inch (6 cm) round cookie cutter, cut out circles; place 2 inches apart on parchment paper–lined baking sheets. These cookies do not spread out at all.
Bake at 325 degrees, rotating pans halfway through until edges are lightly golden, about 8-10 minutes. Let cool completely on pans on racks.
Spread jam on half of the cooled cookies; top with the remaining cookies.