XII: Grilled Peach Upside-Down Cake

From the Rachel Ray Magazine. I have no talent grilling but I'd like to learn :)

5 T unsalted butter
2 1/4 c sugar
1/2 t plus a pinch of salt
1/2 t ground cinnamon
5 large peaches, 4 peeled and thinly sliced, 1 peeled and chopped
3 c flour
1 1/2 t baking soda
2 large eggs
1/2 c vegetable oil
2 t pure vanilla extract
1 c hazelnuts, lightly toasted and coarsely chopped

Build a charcoal fire or preheat a gas grill. In a deep 10-in cast-iron skillet, melt the butter over indirect medium-low heat. Stir in 1/4 c sugar and cook until browned, about 5 minutes. Add a pinch salt, 1/4 t cinnamon and the sliced peaches. Cook until caramelized, about 5 minutes. Arrange the fruit in an even layer in the pan and let cool.
In a medium bowl, toss the chopped peaches with the remaining 2 c sugar and 1/4 t cinnamon. Sift together the flour, baking soda and remaining 1/2 t salt. In a large bowl, whisk together the eggs and oil, then add the vanilla. Gradually stir the flour mixture into the egg mixture until well mixed. Stir in the chopped peach-sugar mixture. Fold in the hazelnuts. Let the batter stand for 15 minutes. Stir the batter again and spread over the cooled fruit in the skillet.
Place the skillet in the center of the grill and bake over indirect medium-low heat, with the lid down, until a toothpick inserted in the center comes out clean, 1.25-1.5 hours. Let cool for 15 minutes. Invert onto a platter and serve warm.