Preheat oven to 375°.
Place blueberries in an 8-inch square baking dish coated with cooking spray.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, milk, and next 4 ingredients in a bowl; stir with a whisk until well blended. Scrape seeds from vanilla bean, and stir seeds into milk mixture. Discard bean, or reserve for another use. Let milk mixture stand 5 minutes. Pour milk mixture over fruit; sprinkle with almonds.
Bake at 375° for 41 minutes or until clafouti is set to the touch in center. Let stand 10 minutes. Sprinkle with powdered sugar just before serving.