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.

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.

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.

Next, mix in the sourdough starter, egg, and vanilla and mix well. Stir in the baking soda and salt until well combined.

Add the flour and mix until almost combined, with a few dry streaks remaining. Add the chocolate chips and stir to combine.

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.

To serve, slice the cookies into individual cookies with a sharp knife. Slice four rows horizontally and four rows vertically to create 16 pieces.