In the bowl of a stand mixer, cream together the butter and sugar until pale and fluffy, 3-5 minutes.

Add in the sourdough discard, eggs, lemon juice, lemon zest, and vanilla extract. Combine until mixed. The mixture will look lumpy.

Add in the flour, baking soda and salt and mix until just combined.

Chill the dough in the fridge for at least 1 hour or up to 24 hours.

Preheat the oven to 350 F.

Line a rimmed baking sheet with parchment paper or a silpat mat.

Scoop 2 Tablespoons scoops of dough onto the prepared baking mat, about 2″ apart.

Bake for 10-12 minutes, until the edges of the cookie are just starting to turn golden brown and the top of the cookies are set.

Allow the cookies to cool on the pan for 5 minutes, and then move to a wire rack.

While still warm, dust with powdered sugar.

Cool completely.