In a bowl, beat together butter, sugar, and vanilla extract until smooth and creamy. In a separate bowl, combine flour and baking powder. Gradually add the dry ingredients to the butter mixture until a smooth dough forms. Fold in walnuts (if using). Refrigerate dough for 1 hour.

Preheat the oven to 325°F (165°C).

Roll dough into 72 small balls. Place each ball 2 inches apart on baking sheets. Press the centers of each ball with your thumb to create wells, and fill the wells with raspberry jam.

Bake cookies in the preheated oven until they turn light golden brown, approximately 18 minutes.

Cool the cookies on the baking sheets for 5 minutes, then transfer them to wire racks to cool completely.