To clean mushrooms, soak quickly in lukewarm water; drain on paper towels. Trim off foot. Make a duxelles using a food processor. Heat up a frying pan, drizzle olive oil and cook duxelles on high for about 4 min. Add shallots, salt and pepper and cook for 3 min more. Add porcini powder and continue to cook on low until dry. Cool and set aside.
Bring water, cream, butter, garlic and rosemary to a simmer. Add in polenta whisking constantly; reduce the heat and let cook on low simmer stirring every so often until cooked - should take 25 min. Add parmesan, and the mushroom duxelles. Readjust seasoning if needed. Transfer polenta in a baking tray lined with plastic wrap. Spread evenly, and cover with plastic wrap in contact; chill for up to 4 days.
Divide chilled polenta into squares or rectangles. Deep fry or pan sear. Enjoy!