Spray a 1-quart microwave-safe casserole dish with cooking spray.
Beat eggs by hand in a bowl until slightly frothy; add flour, sugar, sour cream, and salt. Beat until all ingredients are fully incorporated. Pour batter into prepared casserole dish; sprinkle blueberries over batter.
Microwave on high, turning dish around every minute, until center is set, 4 to 5 minutes. Divide onto plates and sprinkle with confectioners' sugar.