A terrific vegetarian dish, this could easily be rounded out to make a dinner with the addition of a small green salad or some steamed greens. This recipe makes a yellow mountain of soft polenta. What comfort food! For superior flavor, try to find a stone-ground cornmeal with the word polenta on the package. While you are stalking your wild portobellos in the markets, you should have no trouble finding the polenta. Mascarpone, the creamy Italian cheese available in the dairy section of gourmet markets, adds a sweet richness and is absolutely necessary to great polenta.