Preheat oven to 350°F (180°C). Grease an 8” metal square cake pan and line the bottom and sides with parchment. In a microwave-safe bowl, add the chocolate and butter.
Melt the chocolate and butter in the microwave, using 20 second intervals, stirring between each. Generally, 40 seconds total is sufficient. Set aside to cool.
Into another large bowl (or bowl of a stand mixer), add the sugar and eggs.
Using a hand or stand mixer, beat the sugar and eggs together until pale and fluffy, approximately 3 – 5 minutes.
Stir the melted chocolate mixture, vanilla and espresso powder into the egg and sugar mixture and stir until fully incorporated.
Sift the oat flour, cocoa powder, baking powder and salt into the chocolate mixture. Using a spatula, gently stir the mixture until no clumps remain. Break the cookies into large pieces, and fold two thirds of the cookie pieces into the brownie batter.
Pour the mixture into the prepared pan and top with the remaining cookie pieces.
Bake for about 25-30 minutes, or until a cake tester inserted in the centre comes out with a few moist crumbs attached. Let cool in pan on cooling rack. Cut into squares.
Notes
Top Tips
A shiny, crackly top: don’t skip beating the eggs and sugar together, that’s what gives the brownies a shiny, crackly top.
Nice and fudgy: to ensure a fudgy brownie, make sure you don’t overbake them. When testing for doneness, you should have a few moist crumbs clinging to the cake tester / toothpick.
A clean slice: let the brownies cool to room temperature and use a sharp knife to ensure clean slices.
Storage
Brownies will keep 3 – 4 days in an air-tight container at room temperature.