Position an oven rack in the center of the oven and preheat to 350 degrees F.
Melt the butter in a 10-inch cast-iron skillet over medium heat, 2 to 3 minutes, then set aside to cool 5 minutes. Whisk the brown sugar, granulated sugar, vanilla and eggs in a large bowl until smooth. Pour in the butter from the skillet and whisk until combined. Do not wipe out the skillet.
Whisk the flour, cocoa powder, salt and baking soda in a medium bowl. Stir the flour mixture into the egg mixture with a rubber spatula until just incorporated, being careful not to overmix. Stir in all but 1/4 cup of the pecans.
Scrape the dough into the buttered skillet, gently spreading it to the edges and making the top even. Sprinkle the remaining 1/4 cup pecans on top and press lightly with the rubber spatula to make them stick to the dough. Bake until the top is cracked, the edges are slightly browned and crisp and the center is still soft when gently pressed, 40 to 45 minutes. Cool in the skillet on a wire rack for 15 minutes. Cut into wedges and serve warm with ice cream if desired.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
Copyright 2016 Television Food Network, G.P. All rights reserved.