Prepare the Butterbeer Reduction by simmering butterbeer in a saucepan over medium heat for 15-20 minutes until thickened.

Mix Dry Ingredients by whisking together flour, cocoa powder, baking powder, baking soda, and salt in a large mixing bowl.

Combine Wet Ingredients by mixing non-dairy milk, apple cider vinegar, and cooled butterbeer reduction in a medium bowl.

Combine Mixtures by gradually pouring the wet mixture into the dry ingredients, stirring gently until just combined.

Bake by preheating oven to 350°F (175°C), pouring batter into prepared pans, and baking for 30-35 minutes until a toothpick comes out clean.

Cool cakes in pans for 10 minutes before transferring to wire racks to cool completely.

Make Frosting by blending vegan cream cheese, powdered sugar, and butterscotch sauce until smooth.

Assemble the cake by layering cooled cake layers with butterscotch filling and frosting the top and sides.