Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking pan so the cake doesn’t stick.

Mix the cake batter according to the directions on the box, but replace the water with cream soda. (This adds that buttery butterbeer taste.)

Pour the batter into your prepared pan and bake following the time listed on the box.

Remove from the oven and let the cake cool for about 5–10 minutes. It should still be warm but not hot.

Poke holes all over the cake using the handle of a wooden spoon. Space them about 1 inch apart so the pudding can soak in evenly.

Make the pudding. In a medium bowl, whisk together the butterscotch pudding mix and milk for about 1 minute—just until it starts to thicken.

Pour the pudding over the warm cake right away. Gently spread it so the pudding fills the holes and covers the top.

Cover the cake with plastic wrap and place it in the refrigerator for at least 1 hour (overnight is even better). This helps it set and stay moist.

Spread whipped topping evenly over the chilled cake.

Optional: Drizzle with butterscotch sauce or sprinkle crushed toffee bits on top before serving.