Preheat oven to 400 degrees. Combine the carrots, onion, olive oil and garlic in a small bowl, coating the carrots and onions with the olive oil. Spread mixture in a single layer on a baking sheet. Bake until vegetables are tender and have achieved light color, about 45 minutes. Occasionally stir vegetables. Puree the roasted vegetables, lemon juice, and sea salt with enough stock to form a sauce.
Use half parsnips and half carrots in the recipe. Follow same cooking instructions.