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

Cream the softened unsalted butter, brown sugar, and granulated sugar until light and fluffy.

Add the egg, sourdough discard, and vanilla extract, blending until fully incorporated.

Whisk together the flour, baking soda, and salt in a separate bowl, then gradually combine with wet ingredients.

Fold in the blueberries carefully, ensuring they are evenly distributed.

Scoop spoonfuls of dough onto prepared baking sheets, leaving space between each.

Bake for 12–14 minutes until edges are golden and centers look set but slightly soft.

Cool on the baking sheets for about 5 minutes before transferring to a wire rack.

Beat together the cream cheese and softened butter until smooth, then sift in the powdered sugar and mix until fluffy.

Frost cooled cookies generously with the cream cheese mixture.