1. Prepare Oven and Pan:

• Preheat your oven to 350°F (175°C).
• Grease and flour a 9×13-inch baking pan thoroughly. Set aside.

2. Prepare the Cake Batter:

• In a large mixing bowl, combine the yellow cake mix, sour cream, vegetable oil, room temperature eggs, dry instant vanilla pudding mix, 1 cup crushed Oreos, and vanilla extract.
• Mix with an electric mixer (or by hand) on medium speed until all ingredients are well combined and the batter is smooth. Do not overmix.

3. Make the Cinnamon Swirl Mixture:

• In a separate small bowl, combine the packed brown sugar and 1 tablespoon ground cinnamon. If using, stir in the optional ½ cup crushed Oreos for the swirl. Mix well.

4. Layer and Swirl the Cake:

• Pour about half of the prepared cake batter into the greased and floured baking pan, spreading it into an even layer.
• Sprinkle half of the cinnamon-sugar (and Oreo, if using) mixture evenly over this batter layer.
• Carefully pour the remaining cake batter on top of the cinnamon swirl layer, spreading it gently.
• Sprinkle the remaining half of the cinnamon-sugar mixture over the top of the batter.
• Using a knife or a skewer, gently swirl the top cinnamon mixture into the batter below to create a marbled effect. Don’t over-swirl or the layers will completely combine.

5. Bake the Cake:

• Place the pan in the preheated oven.
• Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean or with only a few moist crumbs attached.
• Allow the cake to cool in the pan on a wire rack for about 10 minutes.  
• After 10 minutes, carefully invert the cake onto the wire rack (if desired for frosting all sides, though sheet cakes are often frosted in-pan) or simply let it cool completely in the pan if frosting only the top. Ensure it’s completely cool before frosting.

6. Prepare the Icing:

• Ensure cream cheese is fully softened and heavy cream is very cold.
• In a large, chilled mixing bowl, beat the cold heavy whipping cream with an electric mixer (using whisk attachments) until soft peaks form. Set aside (preferably in the fridge).
• In another large mixing bowl, beat the softened cream cheese with the electric mixer (using paddle attachment or clean beaters) until smooth and fluffy.
• Gradually beat in the sifted powdered sugar and 1 teaspoon ground cinnamon until smooth.
• Beat in the vanilla extract.
• Gently fold the prepared whipped cream into the cream cheese mixture using a rubber spatula until just combined and the frosting is light and fluffy. Be careful not to deflate the whipped cream too much.

7. Frost the Cake:

• Once the cake is completely cool, spread the prepared Cinnamon Cookies n’ Cream Icing evenly over the top of the cake.
• Sprinkle the remaining ½ cup of crushed Oreos decoratively over the top of the icing.

8. Chill (Optional but Recommended) and Serve:

• For best results and easier slicing, cover the cake and refrigerate for at least 30 minutes to an hour to allow the frosting to set slightly.
• Slice into squares and serve. Enjoy your decadent Oreo Honeybun Cake!