Sourdough Fruit Mince Thumbprint Cookies

In a large mixing bowl, add the butter and sugar. Cream the softened butter and sugar together using a whisk.
Now add the egg and egg yolk, vanilla extract and sourdough starter to the butter and sugar mixture and whisk together until smooth.
Next add the flour, baking powder and pinch of salt to the wet ingredients and bring together into a smooth dough. I find a spatula is best for this bit.
Now, cover the dough with plastic wrap and place in the fridge for a minimum of 2 hours. You can leave it in the fridge for up to 48 hours.
When you're ready to bake, preheat the oven to 350F (180C).
Use a tablespoon or cookie scoop to scoop out balls of dough. Roll the balls a little and place them onto the prepared baking trays. I find the balls are perfect around 15g each, but you can go up to 20g.
Use a small spoon (half teaspoon is perfect) to make a small indent in the centre of each cookie. This is the "thumbprint" but a spoon is much easier than using your thumb.
Use a small spoon to place a little fruit mince into the indent in each cookie. You don't want to overfill them or they will make a mess in the oven.
Place the sourdough thumbprint cookies into the oven at 350F (180C) for around 15 to 18 minutes or until they are just golden and the fruit mince is bubbling.
Remove from the oven and allow to sit for 5 minutes on the cookie sheet before transferring to a wire rack to firm up.