Place the skillet on the direct heated grill; allow it to warm for a few minutes. To the pan, add the 4 tablespoons butter, brown sugar and cinnamon. Stir the ingredients with a spoon until well combined and smooth; set skillet aside.

Brush the cut side of the halved peaches with the extra melted butter. Grill peaches cut side-down on clean grates, over direct medium heat, until nicely marked—about 4 minutes. Remove peaches from grill and cool. Grill Serrano chili halves over same heat, until both sides are slightly charred, about 4 minutes. Rough chop the chilies; set aside.

In a medium bowl, sift together the dry ingredients; set aside. Add the vanilla to the buttermilk; set aside.

In a large mixing bowl, beat the butter and sugar together using an electric mixer, creaming well, until light and fluffy. Scrape the bowl down with a spatula. Add the eggs to the butter mixture, one at a time, beating well, and scraping the bowl after each addition. The mixture might take on a curdled appearance, no worries, it will come together. Alternately add the flour mixture and the wet mixture to the butter mixture, beginning and ending with the flour. Intermittently scrape the bowl through the additions.

Tuck a strawberry into the pit cavity of each peach half—you’ll likely need to pare down some of the pointy end of the berry to get a good fit. The end result is to get the cross section of the berry to sit flush in the pit. Carefully arrange the filled peach halves with strawberries, cut side-down on the bottom of the skillet containing the brown sugar mixture. Sprinkle the chopped chili around in the voids left by the peaches.

With a rubber spatula, transfer the cake batter to the skillet. Smooth the top of the batter evenly over the peaches to the edges of the skillet—an offset spatula makes nice work of this. Place the skillet on a sheet pan as an under liner, then transfer to the barbecue grill. Bake the cake over indirect medium heat, maintaining the grill temperature to as close to 350°F as possible, keeping the lid down. The cake is ready when the top is set, golden brown, and a toothpick or skewer inserted in the center comes out clean; about 45 to 55 minutes. Using heavy duty heat pads, remove the skillet from the grill. Cool at room temperature for 10 minutes.

Run a knife around the inside edge of the skillet to loosen the cake. Place an appropriate sized platter over the top of the skillet. Don the heat pads or oven mitts again and invert the skillet onto the platter simultaneously; slowly lift the skillet away. The cake should easily slip out of the skillet. Allow the cake to cool slightly. Cut the cake using a peach half as a serving guide. Serve the cake warm, garnish with a dollop of fresh whipped cream and a sprinkle of fresh basil chiffonade.