Bring 6 cups of water to a rolling boil in a heavy-bottomed 4-quart saucepan over medium-high heat. Reduce the heat to the lowest possible setting, add the baking soda and 1 1/2 teaspoons salt and pour the cornmeal into the water in a very slow stream from a measuring cup, all the while whisking in a circular motion to prevent lumps.
Cook, vigorously stirring the polenta with a wooden spoon for about 10 seconds once every 5 minutes and making sure to scrape clean the bottom and corners of the pot, until the polenta has lost its raw cornmeal taste and becomes soft and smooth, about 30 minutes. If the polenta looks like it's drying out too quickly, continue cooking with the lid on.
Stir in the Asiago, Gorgonzola, mascarpone, butter, Parmesan and garlic. Season to taste with salt and plenty of cracked black pepper. If the polenta is too thick, thin with some milk as desired. Garnish with freshly shaved Parmesan.