Preheat the oven to 400ºF if using convection; otherwise, heat to 425ºF. Place a rimmed baking sheet in oven to preheat for 10 minutes.

In a large bowl, add vegetables, garlic, thyme and olive oil.  Sprinkle with salt and pepper and toss to coat. Carefully, pour the vegetables on the hot baking sheet. 

Place in oven and bake for approximately 30 minutes or until vegetables are caramelized and cooked through. Halfway through the cooking process, add butter to pan and flip the vegetables. The butter will help the vegetables to caramelize. Once done, remove thyme stems and serve.