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

2. Beat butter and sugar together for 2 to 3 minutes until smooth and fluffy.

3. Mix in egg yolk and vanilla extract, then add sourdough discard and stir until combined.

4. Whisk flour, baking powder, and salt in a separate bowl, then fold into the wet mixture until a soft dough forms.

5. Roll dough into 1-inch balls and place 2 inches apart on prepared sheets.

6. Press your thumb or the back of a spoon into each ball to create a well.

7. Spoon about 1/2 teaspoon raspberry jam into each indentation.

8. Bake for 10 to 12 minutes until the edges are light golden, then cool on the tray for 5 minutes before transferring to a wire rack.