Preheat the oven to 375 degrees. Line 9 jumbo muffin tins with paper liners and spray lightly.
Sift the flour, baking powder, baking soda, salt, and cinnamon together in a large bowl.
Stir lightly to be sure the ingredients are combined.
In a 2-cup glass measure, combine the milk, egg, and melted butter.
Make a well in the middle of the dry mixture, pour the wet mixture into the well, and stir until just combined. There will be some lumps but don't overmix the batter!
Combine the blueberries and the sugar and gently stir until the berries are well covered.
Add the berries and sugar to the batter and stir gently to combine.
Using a #12 / 47152 / 2 ¼-inch scoop, spoon the batter into the muffin cups to fill the liners. Sprinkle Demerara sugar on tops.
Bake for 25 minutes, until a cake tester comes out clean and the tops are nicely browned.