In a medium bowl, whisk together the flour, baking powder, and salt. In a small liquid measuring cup, whisk together the milk and the vanilla.
In the bowl of a stand mixer fitted with the paddle attachment, combine the sugar and butter. Beat on medium-high until light, fluffy, and doubled in volume, 2 to 3 minutes, using a rubber spatula to scrape down the bottom and sides of the bowl as necessary. Reduce the mixer to low and add the egg.
With the mixer still on low, add the the dry ingredients in three equal parts, alternating with the wet ingredients in two parts. Beat until just combined, then scrape down the bottom and sides of the bowl once more, then beat on low for an additional 30 seconds. Take half of the blueberries and crush them with your hands so they are juicy; add to the batter and increase the mixer speed to high for 5 to 10 seconds to encourage the berries to release their juices even more. Immediately reduce the mixer to low and add the rest of the berries, mixing until incorporated evenly throughout the batter, another 30 seconds.
Cover the bowl with plastic wrap and let the batter rest at room temperature for 1 hour.
While the batter rests, position a rack in the center of the oven and preheat the oven to 400°F using the convect setting (if possible). Prepare a muffin tin by spraying the inside and border of every other cavity in the muffin tin generously with cooking spray. But note that you’ll only need to prep 4 cavities total—there’s no need to spray the other ones! If you’re using a standard muffin tin, position the pan so that its short side faces you and prep the center cavity of the top row, the outer two cavities of the second row, and the center cavity of the third row.
Use a 1-tablespoon or 3-tablespoon cookie dough scoop to fill each sprayed cavity with 6 tablespoons of the batter. Sprinkle the top of each cavity, aiming for the batter and avoiding the pan, with 1 teaspoon of granulated sugar each. Pour warm water into the outer cavities of the muffin tin’s final row, filling them at least ⅔-rds of the way up. Bake for 22 to 24 minutes, or until the muffins are domed and golden brown around the edges. A skewer inserted into the center of a muffin should come out with a few crumbs attached. Cool the muffins in their muffin tin on a wire rack for 15 minutes, then use an offset spatula to run underneath the edges of the blueberry muffin tops to prevent them from sticking in the pan. Be careful to just run the offset spatula under the edges—you don't want to accidentally cut into the muffin bottom and decapitate the muffin from its top!
After unsticking the muffin tops, keep cooling the muffins in the tins completely to room temperature. DO NOT TRY AND TURN THE MUFFINS OUT WHILE THEY ARE STILL WARM. Because these muffins are so top-heavy, you’ll run the risk of accidentally pulling the tops and bottoms apart if the cake is still warm! Wait until they are cooled completely before turning them out of the pan. Run the offset spatula underneath each muffin top once more and gently tilt the muffin upwards to turn it out of the pan, lifting each one from its base. The muffins are best on the day that they’re made, but can be individually wrapped in plastic and stored at room temperature for up to 2 days.