Heat 2 tablespoons olive oil on medium high. Add onion and leek and sauté until softened. Add garlic and tomato, reduce heat to medium and cook for 10-15 minutes to develop flavors.
Meanwhile, make the basil oil. Blanch the basil in simmering water for 20-30 seconds, transfer to ice bath. Add blanched basil and olive and vegetable oils to a blender and blend on high until smooth. Using cheesecloth or a fine mesh strainer, strain oil from solids. Set aside.
Add stock to pot and bring to a boil. Turn down heat and blend vegetables with stock, season with salt and pepper and serve hot with a drizzle of basil oil.