3 1/2 tablespoons olive oil
1 1/4 pounds zucchini, crookneck or pattypan squash, roughly chopped
1 large onion, chopped
6 cups vegetable stock
1/2 cup julienned basil
1 1/2 tablespoons flour
Salt and freshly ground pepper to taste
Juice of 1 lemon, plus lemon wedges to taste
Chopped scallions, to garnish
Heat 2 tablespoons of the oil in a large saucepan or stockpot, add zucchini and onion. Saute for 5 minutes or until onions are translucent and zucchini is just tender.
Add stock, bring to a boil, reduce heat and partially cover and cook for 25 minutes. Add basil during the last 5 minutes of cooking.
Mix the remaining 1 1/2 tablespoons oil and flour together into a paste. Remove 1 cup of simmering stock and whisk in the roux until smooth. Add back into soup, stir until thickened.
Remove soup from heat to a blender and puree until smooth. Taste and season with salt and pepper. Add lemon juice, and garnish with scallions. Serve with extra lemon slices.