Let the butter melt in a saucepan. Once melted, let it cook further for around 3-4 minutes, stirring occasionally until the milk solids have caramelized and the butter smells nutty. 140 g unsalted butter
Pour the browned butter and all the browned bits, into a large heat-proof bowl. Allow it to cool at room temperature for about 10 minutes, then refrigerate until solidified, but you can still press a finger into it. ** It will be about 112-115g of browned butter.
Once the brown butter has solidified, add the brown sugar, granulated sugar and cream with an electric mixer for around 2 minutes until light and fluffy. 100 g soft brown sugar, 100 g granulated sugar
Next, mix in the sourdough starter, egg, and vanilla and mix well. Stir in the baking soda and salt until well combined. 100 g discard sourdough starter, 1 large egg, 1 teaspoon vanilla extract, 3/4 teaspoon baking soda, ½ teaspoon salt
Add the flour and mix until almost combined, with a few dry streaks remaining. Add the chocolate chips and stir to combine. 190 g all-purpose flour, 170 g semi-sweet chocolate chips
Preheat the oven to 350°F (180°C). Line a 8x8-inch (20x20cm) baking pan with parchment paper.
Scoop the cookie dough into the lined pan. Smooth it out with the back of a spoon or offset spatula
Bake it right away, or cover and chill in the fridge for up to 3 days.
Bake the cookie bars for around 25-28 minutes until the top is set and golden brown.
Let the cookie bar cool in the tin for an hour before removing and letting it cool completely on a wire rack. The cookies will be pretty soft while still warm but will firm up as they cool to room temperature.
To serve, slice the cookies into individual cookies with a sharp knife. Slice four rows horizontally and four rows vertically to create 16 pieces.