Grill-Baked Smoked Ancho Chile Skillet Brownie

In a medium bowl, whisk together flour, cocoa powder, ancho chile powder, baking powder, salt, and cayenne pepper. Serious Eats / Lorena Masso For Heating a Charcoal Grill: Open bottom vent completely. Light chimney starter filled with charcoal briquettes (6 quarts). Once top coals are partially covered with ash, pour into a steeply banked pile against 1 side of the grill. Nestle one 3-inch wood chunk into hot coals. Set cooking grate in place, cover, and open lid vent. Heat until grill is hot (500°F; 260°C) and filled with smoke, about 5 minutes. Serious Eats / Lorena Masso For Heating a Gas Grill: Soak 1 cup wood chips in water for 15 minutes. Drain well. Use a large piece of heavy-duty aluminum foil to wrap chips into foil packet and cut several vent holes in the top. Place wood chip packet directly on primary burner. Turn all burners to high, cover, and heat grill until hot (500°F; 260°C), about 15 minutes. Leave primary burner on high and turn off other burner(s). (see notes) In a 10-inch cast iron skillet, add butter, half the bittersweet chocolate, water, and espresso powder, if using, and place on cooler side of the grill. Cook, swirling skillet and stirring occasionally, until butter is melted and beginning to bubble (some chocolate may not be fully melted). Using grill gloves, remove the skillet from the grill. Serious Eats / Lorena Masso Using a rubber spatula, scrape butter mixture into a large heatproof bowl and set now-empty skillet aside. Add sugar and oil to bowl with butter mixture and whisk until well combined. Whisk in eggs and vanilla until smooth. Serious Eats / Lorena Masso Add flour mixture to butter mixture and use rubber spatula to stir until just combined and no dry flour is visible. Add remaining 3 ounces bittersweet chocolate and stir until evenly distributed. Scrape batter into now-empty ­skillet and spread into even layer. Serious Eats / Lorena Masso Transfer the skillet to the cooler side of the grill, cover grill, and bake, rotating skillet halfway through baking, until toothpick inserted in center comes out with a few moist crumbs attached (be careful not to overbake; brownie will continue to bake as it cools), 50 minutes to 65 minutes. (For a gas grill, adjust primary burner as needed to maintain grill temperature around 425 degrees; if using 3-or-more-burner grill, adjust primary burner and second burner, leaving other burners off.) Transfer skillet to a wire rack and let cool for at least 30 minutes before cutting and serving.