Place one cake on a portable flat surface like a cardboard cake round, the bottom side of a plate, or anything else you have on hand. I used a round wooden surface.
Put that on top of a cake turntable or use your microwave plate and wheel to make a turntable (just take the wheel off, place it on the counter, and then put the microwave plate back on top of it). I didn't have to even out these cakes but do so if necessary.
Scoop out and then spread the Brown Butter Salted Caramel sauce over the pumpkin cake. Get a good layer on. It will drip down the sides of the cake. Once you're satisfied with the amount of caramel, sprinkle some Maldon Smoked Sea Salt over the surface.
Evenly line up the other cake and place it on top. Because of the caramel sauce, the top cake layer tends to slide. Take a wooden skewer and cut it to the appropriate size so that it doesn't stick out beyond the cake. Push it down the middle of the cake to help keep the cake stable.
Place 1 cup of frosting on top of the cake and start spreading it out in an even layer, using a pastry scraper and the turntable to spread the frosting around.
Once the top is frosted, plaster blobs of frosting all over the cake and begin carefully spreading it around. It's okay if some caramel mixes and swirls into the frosting. When all the frosting is on the cake, smooth it out as best as possible by lightly holding a pastry scrapper at a slight angle to the cake and turning the cake around.
Place sage leaves along the bottom edge of the cake. Ring the top of the cake with caramel corn. Pile some caramel corn in the center and drizzle with more of the Brown Butter Caramel Sauce.
Store the cake covered at room temperature for up to 5 days.