Preheat oven to 350 degrees F. Combine flour, baking powder, and a salt. Stir and set aside.
Cream butter with cinnamon and sugar. Add egg and mix until combined. Add vanilla and mix. In a small bowl or liquid measuring cup, stir milk together with lemon juice and zest. Add flour mixture and milk alternately until totally incorporated. Do not over beat.
Grease a 9 x 13 inch baking pan. Pour in batter and smooth the top. Sprinkle fresh blueberries over the top of the cake.
In a separate bowl, combine topping ingredients. Sprinkle over the top of the cake.
Bake cake for 40 to 45 minutes, or until golden brown. (Mine was done after 45 at 325 degrees in my oven). Sprinkle powdered sugar over the top, if desired. Cut into slices and serve.