Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a mixing bowl, cream the softened butter, granulated sugar, and brown sugar for about 3 minutes until light and fluffy.

Add the vanilla extract and eggs, mixing well after each addition until combined.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually mix into the wet ingredients until just combined.

Scoop out portions of dough and roll into 1-inch balls, placing them on the prepared baking sheets. Indent the center of each ball with your thumb.

Fill each indentation with about half a teaspoon of blackberry jam.

Bake for 12 to 15 minutes until the edges are golden and the centers are soft. Let cool before transferring to a wire rack.

Store in an airtight container at room temperature for up to 1 week or freeze for up to 3 months.