1. Preheat oven to 350°F.
2. Spray a 9" round baking pan with cooking oil.
3. Beat butter, sugar and vanilla until light and fluffy. Add eggs and beat well.
4. Reduce speed to low. Add 1 cup of flour, baking powder and salt, mix until smooth.
5. Pour batter into the baking pan.
6. Mix together blueberries, one teaspoon flour and lemon juice. Spoon mixture over batter.
7. Bake 50 minutes or until baked through. Cool in pan for 10 minutes.