Prepare the Baking Pan:

• Preheat the oven to 350°F (175°C).

• Grease and flour a 9×13-inch baking pan, or line with parchment paper for easy removal.

• Tip: Ensure the pan is well-greased to prevent sticking, and use a light-colored pan for even baking.

Make the Cake Batter:

• In a large mixing bowl, combine 1 box (15.25 oz) yellow cake mix, 1 cup sour cream, ½ cup vegetable oil, 4 large eggs, 1 package (3.9 oz) instant vanilla pudding mix, 1 cup crushed Oreos, and 1 tsp vanilla extract.

• Beat with a hand mixer or whisk until smooth and well combined, about 2 minutes.

• Tip: Crush Oreos in a zip-top bag with a rolling pin or food processor to a coarse texture, and scrape the bowl to ensure even mixing.

Prepare the Cinnamon Swirl:

• In a small bowl, mix 1 cup brown sugar, 1 tbsp ground cinnamon, and ½ cup crushed Oreos (if using) until evenly combined.

• Tip: Break up any brown sugar clumps for a smooth swirl, and stir thoroughly to distribute cinnamon.

Layer the Cake:

• Pour half of the cake batter (about 2½ cups) into the prepared baking pan, spreading evenly with a spatula.

• Sprinkle half of the cinnamon swirl mixture evenly over the batter.

• Pour the remaining batter over the cinnamon layer, spreading carefully to cover.

• Sprinkle the remaining cinnamon swirl mixture over the top.

• Tip: Spread batter gently to avoid mixing layers, and ensure the cinnamon mixture reaches the edges for flavor in every bite.

Swirl the Batter:

• Use a knife or skewer to gently swirl the batter and cinnamon mixture in a figure-eight or zigzag pattern, creating a marbled effect without fully mixing the layers.

• Tip: Swirl lightly to maintain distinct layers, and avoid over-swirling to keep the cinnamon concentrated.

Bake:

• Bake in the preheated oven for 30–35 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.

• Check for doneness: the cake should spring back lightly when pressed.

• Tip: Rotate the pan halfway through if your oven has hot spots, and cover with foil if the top browns too quickly after 25 minutes.

Cool the Cake:

• Remove the cake from the oven and let cool in the pan for 10 minutes.

• Transfer to a wire rack (if removing from the pan) or leave in the pan to cool completely, about 1 hour.

• Tip: Cool completely before icing to prevent the frosting from melting, and run a knife around the edges if removing from the pan.

Prepare the Cinnamon Cookies n’ Cream Icing:

• In a large mixing bowl, beat 1 cup heavy whipping cream with a hand mixer until soft peaks form, about 2–3 minutes.

• In another bowl, beat 8 oz softened cream cheese, 1 tsp vanilla extract, 2 cups powdered sugar, and 1 tsp ground cinnamon until smooth, about 2 minutes.

• Gently fold the whipped cream into the cream cheese mixture with a spatula until fully combined and fluffy, about 1 minute.

• Tip: Soften cream cheese at room temperature for 30–60 minutes for easy mixing, and chill the icing briefly if it softens too much.

Frost the Cake:

• Once the cake is completely cool, spread the icing evenly over the top using an offset spatula or spoon, creating a smooth or swirled finish.

• Sprinkle ½ cup crushed Oreos evenly over the icing for added crunch and visual appeal.

• Tip: Spread icing gently to avoid lifting cake crumbs, and crush Oreos to a fine texture for a neat topping.

Serve:

• Slice into 12–15 squares or rectangles using a sharp knife, wiping the blade between cuts for clean edges.

• Serve at room temperature or slightly chilled, optionally with coffee, milk, or hot cocoa.

• Tip: Use a spatula to lift slices cleanly, and serve on a platter to showcase the swirls and Oreo topping.