In a small bowl: mix milk and lemon juice, set aside
In a large bowl: combine flour, sugar, baking powder, cinnamon,and salt.
Add egg (lightly beaten) and oil to the milk mixture; mix well, then add this to the flour mixture just until moistened (it will be thick). Fold in blueberries. (Recipe calls for 1 cup, but I always add more.)
Fill greased or paper-lined muffin cups two thirds full. Bake at 400 degrees F at 25 minutes or until center bounces back when lightly touched.