Preheat your oven to 350°F and prepare a baking sheet with parchment paper.

In a medium mixing bowl, whisk together your flour, baking powder, and salt - set aside.

In a large mixing bowl using a hand mixer or in a bowl of a stand mixer, mix the softened butter and sugar until it becomes light and fluffy.

Add the sourdough starter, egg, and vanilla extract. Mix until combined.

Add the flour, baking powder, and salt to the wet ingredients and use the mixer to incorporate them until just mixed. Use a spatula or large wooden spoon to scrape the sides of the bowl, combining all of the ingredients.

Take a gracious amount of granulated sugar and pour it on a small plate or in a small bowl. Use a cookie scoop or tablespoon measuring spoon to measure out your dough and shape it into a ball.

Gently roll it in the granulated sugar to lightly coat. I like to leave some of my cookies uncoated as well. Place the dough ball on a greased or parchment-lined cookie sheet and use your thumb or small spoon to make your desired indention.

Fill your small indent with a 1/2 teaspoon of jam

Bake the cookies for 14 minutes.

Remove from the oven and allow them to cool before placing them on a cooling rack.

Once the cookies have cooled completely, you can lightly sprinkle them with powdered sugar or leave them as is.