In a large heavy saucepan, heat the olive oil over low heat. Add the garlic and onion and sauté stirring constantly, for about 3 minutes, or until softened. Do not let the garlic burn.

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 polenta 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.

Mound the polenta into the pan and, using a rubber spatula repeatedly dipped in very hot water, spread the polenta 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.

Preheat a broiler to high heat. Brush the broiler pan with oil.

Cut the polenta 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.