• 2/3 cup unsalted butter, at room temperature
• 1 cup packed brown sugar
• 1 teaspoon vanilla extract
• 3 1/2 cups all-purpose flour
• 1/2 teaspoon baking powder
• 1/2 teaspoon baking soda
• 3/4 cup chocolate chips
• 2 tablespoons vegetable oil
• In a large mixing bowl, cream together the butter, sugars and vanilla. Sift in the flour, baking powder, baking soda and salt and mix together well with an electric mixer. Add the egg and mix that through, then add the chocolate chips and stir it together with a wooden spoon.
• Divide the cookie dough into 16 pieces and shape them into firm balls. Chill in the fridge for one hour. Preheat the oven to 375 degrees. Line 2 large trays with baking parchment, and place the cookie balls evenly spaced out. Bake for 18 minutes, then remove from the oven and leave to cool on the tray for 10 minutes before transferring to a wire rack.
• Mix together the brownie mix with enough oil and water to bring it to a runny consistency. Fill a plastic syringe with the cookie batter then inject it into each cookie. Serve immediately.