In a large bowl, mix 1 1/4 cups (150g) flour, 1/2 cup (100g) sourdough starter, 1/2 cup (50g) cocoa powder, 1/2 tsp (3g) baking powder, 1 tsp (7g) baking soda, 1/4 tsp (3g) salt, 1 cup (200g) sugar, 2/3 cup (150g) softened butter, and 1 egg until a dough forms. Place the dough  into a bowl and place into the fridge for around 4 To 12 hours (it can go up to 48 hours though).

Preheat your oven to 190C. Roll the dough into 1-inch balls and place on a baking sheet and gently press the dough balls flat. Bake at 350°F (175°C) for 12 minutes. Cool completely on a wire rack. 🍪🔥⏲️

For the filling, beat 1/2 cup (110g) softened butter, 1 tsp (5g) vanilla extract, 2 3/4 cups (315g) powdered sugar, and 1/2 tsp (3g) salt until smooth and creamy. 🧈🌸🍬🧂

Spread a generous layer of filling on the flat side of half the cookies. 🍫

Top with the remaining cookies to form sandwiches. Serve and enjoy. 🍪🍽️