Preheat oven to 350°F (175°C).

In a large bowl, cream together the softened butter and sugar until light and fluffy.

Beat in the eggs one at a time, then stir in the vanilla.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Roll the dough into 1-inch balls and place them on a baking sheet lined with parchment paper.

Make an indentation in the center of each ball using your thumb. Fill each indentation with jam.

Bake for 12-15 minutes, or until the edges are lightly golden brown. Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.