Gently wash the squash flowers, break off stems and pluck out the stamens. Peel 1 zucchini and cut in thick slices. Cut the other (unpeeled) in small dice. Shuck the corn and cut off and reserve kernels and scraped cobs. Peel the potato and cut in chunks.
Melt the butter in a medium saucepan over medium-low heat. Cook the onion, covered, until translucent but not browned. Reserving 6 squash blossoms for garnish, stir in the rest. Add half the corn kernels, the cobs and the potato. Cover with chicken broth. Bring to a simmer and cook, partly covered, until vegetables are very tender, about 25 minutes. Remove corn cobs. Stir in the cream. Cool until warm. Using a blender, puree the soup until smooth. Season with salt and roasted or ground red pepper to taste, blending briefly.
Return the soup to the saucepan. Stir in the diced zucchini, corn kernels and cornstarch slurry. Reheat gently until the vegetables are cooked and the soup thickens. Spoon into bowls, topping each with a squash blossom and, if using, fried tortilla strips.