Preheat the oven to 160ºC /320ºF conventional oven. Prepare a 20x20 cm square pan with parchment paper.
Melt the butter and add chocolate chips to the butter. Let it melt together until smooth.
90 g butter, 75 g dark chocolate chips
Sift together the flour, cocoa powder, cornstarch and salt.
75 g all-purpose flour, 35 g cocoa powder, 1 tablespoon cornstarch, ½ teaspoon salt
In a bowl, with an electric hand mixer, whisk together the eggs, brown sugar and granulated sugar until light and fluffy for 4 minutes. Add the melted butter and chocolate, oil and vanilla extract into the batter and mix until combined.
130 g granulated sugar, 130 g brown sugar, 3 large eggs, 70 g oil, 1 ½ teaspoon vanilla extract
Add flour mixture to the batter and on the lowest setting gently mix it together until combined. Scrape down the sides of the bowl with a spatula.
Pour half the batter into the prepared baking pan, smooth it out with the spatula. Heat up the peanut butter for 1 minute in the microwave so it is more fluid. Pour the peanut butter over the brownie batter and spread it out. Add 15 mini peanut butter cups, cut in half. Then add the other half of the brownie batter and even it out.
100 g smooth peanut butter, 15 Reese’s mini peanut butter cups
Bake for about 45-50 minutes.
Immediately out of the oven drizzle with extra peanut butter and halved mini peanut butter cups. Let it cool down completely on a cooling rack.
50 g peanut butter, 15 Reese’s mini peanut butter cups
Serve once it’s cooled down.