Preheat oven to 425℉ (220℃) conventional (see note 1 if using a convection oven) and line a 12-hole standard muffin tray with muffin liners. Set aside.
Prepare the cinnamon sugar topping by mixing the sugar and cinnamon in a small bowl. Stir well and set aside.
Next, sift together the flour, baking powder, and salt. Using a whisk, mix until well combined, then set aside.
In a large bowl, combine the sugar, egg, butter, vegetable oil, milk, vanilla, lemon zest, and lemon juice. Using a whisk, mix until well combined.
Add the pre-sifted dry ingredients to the wet ingredients, and using a spatula, gently fold until just combined. Do not overmix.
To finish off the batter, add in 1 cup (150g) of the blueberries and gently fold with a spatula until just combined. Do not overmix.
Distribute the batter evenly among the muffin liners—they should be about ¾ full. Evenly sprinkle the cinnamon sugar mixture prepared earlier on top. Finish by dotting the remaining ½ cup (75g) of blueberries over the tops of the muffins, gently pressing them into the batter while keeping them visible.
Bake for 8 minutes at 425℉ (220℃). Then, without removing the muffins from the oven, reduce the temperature to 350℉ (180℃) and bake for an additional 10–12 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the muffins cool in the tray for 10 minutes before transferring them to a wire rack to cool completely. Enjoy!