1-Preparing the Cake Layers: Preheat oven to 180°C (350°F) conventional. Grease and line bottoms of two 8-inch cake pans.

2-Preparing the Cake Layers: Sift together 2⅓3 cups all-purpose flour, ¼ cup cornstarch, ½ tsp baking soda, 2 tsp baking powder, ½ tsp salt, and 1 tsp ground cinnamon. Mix to combine and set aside.

3-Preparing the Cake Layers: Cream ½ cup unsalted butter, ½ cup vegetable oil, and 1¼ cups firmly packed soft light brown sugar with an electric mixer for 2 minutes until light and creamy.

4-Preparing the Cake Layers: Add 3 large eggs one at a time, mixing well between each addition.

5-Preparing the Cake Layers: Mix in ½ cup cookie butter and 2 tsp vanilla extract.

6-Preparing the Cake Layers: Add half of dry ingredients and fold gently until just combined. Add 1¼ cups buttermilk and fold again. Add remaining dry ingredients and fold gently; do not overmix.

7-Preparing the Cake Layers: Break 15 individual plain cookies into small chunks and fold into the batter.

8-Preparing the Cake Layers: Divide batter evenly between cake pans, level tops, and tap pans to remove large air bubbles. Bake for 37-40 minutes, or until a toothpick inserted comes out clean or with a few moist crumbs.

9-Preparing the Cake Layers: Cool cake layers in pans for 20 minutes, then loosen edges and transfer to a wire rack to cool completely.

10-Making the Cookie Butter Frosting: Blend 15 individual plain cookies into fine crumbs; set aside.

11-Making the Cookie Butter Frosting: Combine 2⅛ cups powdered sugar, 1½ cups unsalted butter, 1½ tsp vanilla extract, ¼ tsp salt, and 1½ tbsp milk in a large bowl.

12-Making the Cookie Butter Frosting: Mix on low speed until combined, then increase speed to medium-high and beat for 10 minutes, scraping the bowl halfway through, until light, fluffy, and smooth.

13-Making the Cookie Butter Frosting: Add ¼ cup cookie butter and cookie crumbs; mix on medium speed until well combined.

14-Assembling the Biscoff Cookie Butter Cake: Slightly heat ⅜ cup cookie butter to soften, then let cool to a spreadable consistency.

15-Assembling the Biscoff Cookie Butter Cake: Level cake layers with a serrated knife, optionally trimming caramelized edges.

16-Assembling the Biscoff Cookie Butter Cake: Place first cake layer on a stand and spread a generous layer of buttercream, smoothing it out.

17-Assembling the Biscoff Cookie Butter Cake: Pipe a dam of frosting around the edges with a 1M piping tip. Fill the center with half of the cookie butter (about 1/3 cup), making sure the cookie butter is not warm to prevent melting the frosting.

18-Assembling the Biscoff Cookie Butter Cake: Add the second cake layer, cover the sides and top with remaining buttercream, leaving some for piping decoration. Smooth the sides with a cake scraper.

19-Assembling the Biscoff Cookie Butter Cake: Pipe a border on top, fill the center with remaining cookie butter, and decorate with additional plain cookies.