Preheat the oven to 350º.
Mix the cake batter as directed on the box.
In the largest skillet you have, melt the butter over medium heat. It's important that the skillet be oven safe and have a flat bottom.
Carefully pour the batter into the skillet and smooth it out.
Bake, uncovered, at 350 for 30 to 35 minutes, or until a cake tester inserted in the center comes out clean.
While the cake is baking, mix the frosting with the caramel. Set aside.
When the cake is done, flip it onto a large platter. While the cake is hot, pour enough of the frosting to completely cover the top (which was the bottom before you turned it out) onto the cake and smooth it out. The frosting will melt, soak into the cake, and run all over the place, making a gooey and delicious mess. This is why you put it on a platter and not on a plate.
Allow the cake to cool for 15 to 30 minutes, until it's warm but no longer hot. Pour the rest of the frosting onto the cake and smooth it out. Sprinkle the nuts over top. You can garnish with a little extra caramel if you're so inclined.
This is delectably rich, so I serve it with ice cream.