creamy white polenta with mushrooms

INGREDIENTS

• 4 1/2 cups water
• 1 cup coarse stone-ground white grits (preferably organic)
• 1/4 cup heavy cream
• 2 tablespoons finely grated Parmigiano-Reggiano
• 1 teaspoon salt
• 1/4 teaspoon black pepper
• 1 pound assorted fresh exotic mushrooms such as porcini, oyster, chanterelle, lobster, and hedgehog
• 3 tablespoons extra-virgin olive oil
• 1 garlic clove, smashed
• 1/2 teaspoon salt
• 1/4 cup water
• 3 tablespoons cold unsalted butter
• 1 1/2 tablespoons fresh lemon juice
• 1 tablespoon chopped fresh flat-leaf parsley (we used chives)
• 1/2 cup mascarpone (though we used crème fraîche, and just a tad)