Melt the butter in a microwave or the stove, then let it cool to room temperature. 140 g butter
To the melted butter, add the sugars, vanilla, egg, and sourdough starter. Mix it together well. The sourdough starter may be tricky to mix in initially, but keep stirring until combined. 100 g soft brown sugar, 100 g granulated sugar, 100 g discard sourdough starter, 1 large egg, 1 tsp vanilla extract
In a separate bowl, mix the flour, baking soda and salt. Add to the wet ingredients and stir it all together until combined. 225 g all-purpose flour, 3/4 tsp baking soda, 1/4 tsp salt
Stir in the chocolate chips. It will be a very sticky dough. 170 g semi-sweet chocolate chips
Chill the dough for at least 2 hours or up to 2 days.
Preheat the oven to 180°C/ 350°F.
Line two cookie sheets with baking paper. Roll the cookie dough into 16-18 balls of around 1 1/2 tablespoons of dough.
Space the cookie balls about 3cm apart on the baking sheets. Bake for approximately 10-12 minutes until the edges of the cookies are light golden brown, but the tops are still pale.
Let them cool for 5 minutes on the baking sheet before placing them on a wire rack to cool further.
Notes
Both metric and US customary measurements are provided. Use the toggle on the recipe card to switch between the two.