Preheat the oven to 350 degrees F (175 degrees C).

Cream sugar and butter with an electric mixer until fluffy, about 5 minutes. Mix in egg and vanilla extract. In a separate bowl, combine flour, baking powder, and salt. Add the dry mixture to the butter mixture and mix well.

Put a handful of the dough between two sheets of parchment paper and roll to desired thickness. Repeat with the rest of the dough. Place the rolled dough on a cookie sheet with the parchment paper and refrigerate for 10 minutes or longer. Repeat the process with scraps after cutting cookies.

Cut 24 heart-shaped cookies of the same size from the dough. Use a smaller heart-shaped cookie cutter to cut a second hole in half of the cookies. Transfer the cut cookies to a baking sheet.

Bake cookies in the preheated oven until edges are golden, about 8 to 10 minutes.

Transfer the baking sheet to a wire rack to cool for 20 to 30 minutes. Spread about 1/2 teaspoon of jam into the centers of the whole cookies without the heart-cut centers.