In a large skillet over medium heat, saute onions in 2 tablespoons butter, stirring occasionally 15-20 minutes until onions are caramelized and tender. Increase heat to medium-high and add mushrooms to skillet, stirring occasionally until mushrooms are tender. Transfer onion-mushroom mixture to a bowl and set aside.

In same skillet, saute garlic in remaining 1 tablespoon butter until fragrant. Add rice to skillet and stir 1 minute. Add vinegar, then reduce heat to medium and begin adding hot chicken broth to rice, a little bit at a time, waiting until liquid is evaporated before adding more broth. Continue adding broth in small amounts 10-15 minutes until rice is tender and creamy. Stir in half-and-half, onion/mushroom mixture, and season risotto with salt and pepper to taste. Garnish with fresh parsley and serve risotto warm and enjoy!