In a large heavy saucepan, heat the olive oil over medium low heat. Add the red onion and saute, stirring constantly, for about 3 minutes, or until softened. Add the garlic and cook for 1 minute more. Add the chicken stock, water, and salt and bring to a boil over medium high heat. Reduce the heat and, when the liquid is simmering, gradually sprinkle the pollinate over in a very slow, thin stream, whisking constantly in the same direction until all the grains have been incorporated and no lumps remain. Reduce the heat to very low.
Switch to a wooden paddle and stir thoroughly every 1 or 2 minutes for 25 to 30 minutes, or until the mixture pulls away from the sides of the pan and the grains of pollinate have softened. Stir in the black pepper, cotija, and butter. The mixture will be quite thick.
Rinse an 8 x 12 inch roasting pan with water and shake dry. Mound the pollinate into the pan and, using a rubber spatula repeatedly dipped in very hot water, spread the pollinate evenly in the pan until it is just under 1/2-inch thick. Cover with a tea towel and allow to rest for 1 hour at room temperature or up to 24 hours in the refrigerator.
When ready to serve, preheat a broiler to high heat. Brush the broiler pan with oil. Cut the pollinate into 8 equal squares and brush them with olive oil. Transfer the squares to the broiler pan and grill for about 8 minutes on each side, or until deep golden brown. Serve immediately.
c.1997, M.S. Milliken & S. Feniger, all rights reserved