For tomato sauce:
1 garlic clove, minced
1/4 teaspoon hot red pepper flakes
2 tablespoons olive oil
1 1/2 pound plum tomatoes, finely chopped
1/2 cup water
1/2 teaspoon sugar
1 cup whole-milk ricotta (preferably fresh)
1 large egg yolk
1/4 cup finely chopped mint
2/3 cup grated Parmigiano-Reggiano, divided
12 to 16 large zucchini squash blossoms
1/2 cup plus 1 tablespoon all-purpose flour
3/4 cup chilled seltzer or club soda
About 3 cups vegetable oil for frying
Make tomato sauce:
Cook garlic and red pepper flakes in oil in a 2-quarts heavy saucepan over medium heat, stirring, until garlic is golden, about 30 seconds. Add tomatoes, water, sugar, and 1/2 teaspoon salt and simmer, uncovered, stirring occasionally, until thickened, 25 to 30 minutes.
Prepare squash blossoms:
Stir together ricotta, yolk, mint, 1/3 cup parmesan, and 1/8 teaspoon each of salt and pepper.
Carefully open each blossom and fill with about 2 rounded teaspoon ricotta filling, gently twisting end of blossom to enclose filling. (You may have filling left over.)
Heat 1/2 inch oil to 375°F in a 10-inch heavy skillet. Meanwhile, dip half of blossoms in batter to thinly coat. Fry coated blossoms, turning once, until golden, 1 to 2 minutes total. Transfer with tongs to paper towels to drain. Coat and fry remaining blossoms. (Return oil to 375°F between batches.) Season with salt. Serve with tomato sauce.
Cooks' Note:
Tomato sauce and ricotta filling can be made 1 day ahead and chilled. Reheat sauce before serving.
