Preheat the oven to 350°F (175°C). Line an 9X13-inch square baking pan with parchment paper or lightly grease it to prevent sticking.
Prepare the dry ingredients: In a medium bowl, whisk together the cocoa powder, flour, and salt. Set this mixture aside for later.
1 cup Cocoa Powder, 3/4 tsp. Salt, 1 cup Flour
Mix the wet ingredients: In a large bowl, whisk together the melted butter, vegetable oil, light brown sugar, and granulated sugar until smooth and well combined. Stir in the vanilla extract. Add the eggs and egg yolk, one at a time, mixing until fully incorporated after each addition.
3/4 cup Butter, 1/4 cup Canola Oil, 1 & 1/4 cup White Granulated Sugar, 1/2 cup Brown Sugar, 2 tsp. Vanilla Extract, 2 large Eggs, 1 Egg Yoke
Combine wet and dry ingredients: Gradually fold the dry ingredients into the wet mixture using a spatula or a wooden spoon. Mix until just combined—be careful not to overmix.
Add chocolate chips: Gently fold in the chocolate chips, ensuring they are evenly distributed throughout the batter.
1/2 cup Chocolate Chips
Pour the brownie batter into your prepared pan and spread it out evenly. Smooth the top with a spatula.
Melt the Biscoff Cookie Butter: In a microwave-safe bowl, microwave the Biscoff Cookie Butter for 20-30 seconds, or until it is soft and slightly runny. Stir it to ensure it’s smooth and melted.
1/4 cup Biscoff Cookie Butter
Swirl the cookie butter: Drizzle the melted Biscoff Cookie Butter over the top of the brownie batter in the pan. Using a knife or a toothpick, gently swirl the cookie butter into the batter in a marble pattern, creating beautiful streaks throughout
Place the pan in the oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). Keep an eye on the brownies as baking times may vary slightly depending on your oven.
Allow the brownies to cool in the pan on a wire rack for about 1 hour. This helps them set and makes cutting easier.
Once completely cool, cut into squares and enjoy the irresistible combination of fudgy brownies and spiced cookie butter swirls!