01 - Preheat the oven to 425°F (220°C).
02 - On a large baking sheet, toss mushrooms with olive oil, garlic, thyme, salt, and pepper. Spread in a single layer.
03 - Roast mushrooms for 20–25 minutes, stirring once halfway, until golden and tender.
04 - Meanwhile, in a large saucepan, bring water and milk to a simmer over medium heat.
05 - Slowly whisk in the polenta, stirring constantly to prevent lumps.
06 - Reduce heat to low and cook, stirring frequently, for 20–25 minutes or until thick and creamy.
07 - Stir in butter, Parmesan, salt, and pepper. Taste and adjust seasoning as desired.
08 - Spoon creamy polenta into bowls or plates. Top with roasted mushrooms and any pan juices.
09 - Garnish with chopped parsley and extra Parmesan if desired. Serve immediately.