• Butter a 9-inch square baking pan and set it aside. Preheat your oven to 325°F.

Make the corn muffin mix

• In a medium-size bowl, place the flour, xanthan gum, cornmeal, sugar, baking powder and salt, and whisk to combine well.
• Add the shortening and, with the tines of a fork cut the coconut oil into the dry ingredients until the mixture resembles coarse sand. There will be some clumps.
• Set the bowl aside.

Make the casserole

• In a small dry pan, sauté the optional pancetta in a hot pan over medium heat until cooked through (about 5 minutes), then drain off the rendered fat.
• Add the optional diced jalapeño and sauté for 1 minute, just until starting to soften. If you're not using the pancetta, add 1 tablespoon olive oil to the pan to cook the pepper and 1/4 teaspoon extra kosher salt. Set the mixture aside to cool.
• Drain the liquid from one can of corn, reserving 1/2 cup (4 fluid ounces) of the liquid. Place the corn and reserved liquid into a food processor or blender and pulse until the corn is a chunky, loose mixture. Set it aside.
• To a large mixing bowl, add the sour cream, melted butter and eggs, and whisk until well-combined and very pale yellow and smooth.
• Drain as much liquid as possible from the other can of corn, and add it and the processed corn to the large mixing bowl. Mix to combine. The mixture will be loose.
• Add the cooked pancetta and jalapeño to the bowl with the corn muffin mixture. Add about 1/2 cup of the optional shredded cheese, if using, to the same dry ingredient mixture, and toss everything to combine.
• Add everything in the medium mixing bowl to the large mixing bowl with wet ingredients, and mix until just combined. The mixture will be thick but very soft.
• Transfer the mixture to the prepared baking pan, and smooth into an even layer.

Bake

• Bake in the center of the oven for about 45 minutes, or until the top is lightly golden brown and mostly firm to the touch.
• If you’re omitting the cheese, rotate the dish in the oven and continue to bake for another 10 minutes until a tester comes out mostly clean (not wet, but a few moist crumbs are okay).
• If you’re the shredded cheese on top, remove the dish from the oven and increase the oven temperature to 350°F.
• Scatter the cheese on top in an even layer. Return the pan to the center of the oven to bake for about another 10 minutes, or until the top is golden brown and a tester comes out mostly clean (not wet, but a few moist crumbs are okay).
• Let the finished casserole stand for at least 10 minutes before sprinkling with chopped chives, slicing into 9 equal pieces, and serving.