Preheat oven to 400°F. Place onions, garlic, jalapeños, carrot and potato into a large mixing bowl and drizzle with oil. Mix to coat well and pour onto a parchment-lined sheet tray. Roast in preheated oven for 25-30 minutes or until all vegetables are fork tender. Remove and let cool for 10 minutes. Add roasted vegetables, seasonings, milk and vegetable stock to the Vitamix container in the order listed and secure the lid. Start the blender on its lowest speed, then quickly increase to its highest speed. Blend for 1 minute or until desired consistency is reached. Serve immediately.