Preheat the oven to 350 (F).

In a large bowl, whisk together 1 cup flour, 1 cup sugar, 1/2 teaspoon baking soda, and a dash of salt together. Set aside.

In your 10-inch cast iron skillet, bring 4 tablespoons butter, 1/4 cup vegetable oil, 2 tablespoons cocoa powder, and 1/2 cup water to a boil:

Remove from heat.

Whisk in the dry ingredients (from the first step) into the butter/oil/cocoa powder mixture. At first the mixture will be clumpy, but with enough whisking the ingredients will incorporate together to create a smooth, thick batter:

Using a rubber spatula, mix in the buttermilk, egg, and vanilla:

Don't rush this process. You're basically forcing more liquid into an already fatty mixture that doesn't want to make room for the liquid. There should be no streaks of fat or liquid before you move on to the next step:

I found the most effective way of mixing was to actually fold the ingredients together. That way, I didn't get batter running out the sides of the skillet from violent mixing.

As the cake starts to cool, make the frosting. In a medium saucepan, melt 4 tablespoons butter.

Remove from heat and add 2 cups powdered sugar, 1/2 cup chopped pecans, and 1/2 teaspoon vanilla. Stir to combine, making sure that all the powdered sugar lumps have been disintegrated by the chopped pecans.

Once the frosting is ready, pour over the warm cake and spread with a spatula. The frosting will initially appear to liquidy, but will harden as the cake cools.