Saute the chorizo: In a large pan add the butter, chorizo, onion and garlic. Saut while stirring to keep the onions from browning until the chorizo is cooked through and broken down to resemble ground meat, about 10 minutes. Pour into a large bowl and allow to cool while working on the rest.
Prepare the cornmeal: In a medium pot on medium heat, add the cornmeal, milk and buttermilk. Bring to a simmer while whisking to keep the cornmeal from clumping or sticking in the corners of the pot. When the liquid begins to thicken, turn off the heat and continue to stir until its the texture of loose grits or oatmeal.
In a small, steady bowl whisk the eggs while very slowly adding a spoonful of the cornmeal mixture. Whisk vigorously to combine and feel the outside of the bowl. If its not warm, add some more cornmeal mixture while continuously whisking, and keep adding the cornmeal mixture until the eggs are just as warm as the cornmeal mixture. Then reversing the order, slowly pour the egg mixture into the cornmeal mixture, whisking vigorously.
Preheat the oven to 400F. Pour the cornmeal and egg mixture into the large bowl of cooked chorizo. Add the green chilies, cheddar cheese, mozzarella cheese, corn and scallions. Stir to combine. Butter the bottom and sides of a 9x13-inch dish. Pour in the batter and bake in the oven until the edges are golden brown and the center is set, about 25 to 30 minutes. Serve hot.