Prep the vegetables: Dice the onion, mince the garlic, and slice the mushrooms.
Optional sauté step: In a skillet, heat butter or oil and sauté onion and garlic until fragrant. Add mushrooms and cook 3–4 minutes. This step boosts flavor but may be skipped.
Add ingredients to crockpot: Place Arborio rice, mushrooms, onions, garlic, broth, wine, salt, pepper, and thyme into the slow cooker.
Mix gently: Stir to distribute everything evenly.
Slow cook: On HIGH: Cook 2–2.5 hours. On LOW: Cook 3–4 hours.
Stir once halfway if possible, but not essential.
Finish risotto: When rice is tender and creamy, stir in Parmesan and the remaining butter. Adjust seasonings.
Rest: Let risotto sit 5 minutes to thicken.
Garnish: Add chopped parsley if desired.