Place cauliflower in a microwave-safe bowl. Heat in the microwave until softened, about 1 minute.
Pulse cauliflower in a food processor into small pieces roughly the size of rice.
Heat olive oil in a skillet over medium heat. Melt butter in the skillet and add cauliflower, salt, pepper, and onion powder. Add mushrooms and milk; bring to a boil and add white wine. Reduce heat and simmer until sauce thickens, about 10 minutes.