In a medium saucepan or deep saute pan with a heavy base, bring 1.6 litres of cold water to a boil, add salt, stir and reduce to a lively simmer.
Slowly “rain” in the polenta, whisking as you do so to prevent it clumping.
Once the polenta is incorporated, swap the whisk for a wooden spoon and stir, very regularly, for 45 minutes, or until the polenta is thick but not stiff (if that is the case, add more hot water), pulling away from the sides of the pan and cooked through.
Beat 50g butter, the milk and the cheese into the polenta, adding a little more milk, if necessary, to loosen it to a soft, spoonable consistency.
Meanwhile, melt the remaining butter and the olive oil, and warm the whole garlic clove.
Add the mushrooms, saute until soft, then add the minced garlic and parsley, and season to taste.
Spoon the polenta on to a large serving dish or board, or several individual ones, and top with the mushroom mix.
Serve, passing around extra grated cheese for those who want it.
