Melt 2 tablespoons butter in a large saucepan over medium heat. Add the onion and garlic and cook until the onion is translucent, about 5 minutes. Add the chicken stock and bring to a simmer.
Slowly whisk in the polenta. Reduce the heat to low and cook, stirring frequently, until the polenta is thick, about 2 hours (adjust the consistency with water or stock, if necessary).
Remove from the heat and whisk in the mascarpone, parmesan and the remaining 4 tablespoons butter. Season with salt and pepper and garnish with parsley.
Photograph by Jim Franco
Courtesy of Michael Symon for Food Network Magazine