In a mixing bowl, beat the butter and sugar until light and fluffy, about 3-4 minutes
Add the egg and vanilla, mixing until smooth
Stir in the sourdough discard until fully combined
In a separate bowl, whisk together the flour and baking powder
Gradually fold the dry ingredients into the wet mixture until a soft dough forms
Cover the dough and refrigerate for at least 1 hour (or up to 24 hours)
Preheat the oven to 180°C (350°F) and line a baking tray with parchment paper
Roll small portions of dough (about 1 tablespoon each) into balls
Place dough balls on the prepared tray, leaving space between each
Use your thumb or a spoon to press a small indentation in the center of each cookie
Fill each indentation with your chosen jam
Bake for 12-15 minutes, or until lightly golden around the edges
Let cool on the baking tray for 5 minutes, then transfer to a wire rack to cool completely
