Preheat oven to 400°F and set oven racks to the top and lower thirds.

Line two 12-cup muffin tins with either 10 jumbo-size liners, staggering them in a diamond shape, or 15 regular liners.

In a large bowl, whisk together the flour, baking powder, salt, cinnamon, nutmeg, and sugars.

In a small bowl or liquid measuring cup, combine the milk, sour cream, eggs, and vanilla. Whisk in the butter until homogenous.

Add the liquid mixture into the dry ingredients. Fold just until a few streaks of flour remain.

Gently fold in the blueberries until evenly dispersed, which should bring the batter together and incorporate any remaining dry ingredients. Don't over-mix; a few small lumps are okay.

For jumbo muffins, fill each liner with about 5 to 6 tablespoons of batter (125 grams), almost to the top. For regular muffins, fill each liner with 3-4 tablespoons (80 grams).

Dot the tops of each muffin with a few more blueberries, then generously sprinkle granulated sugar on top.

For jumbo muffins, bake on the top and lower racks for 24 to 25 minutes (around 22 minutes for regular size) rotating the pans and switching their positions halfway through. The edges should be golden brown and the top should spring back when gently pressed.

Let cool in the tins for about 5 minutes then carefully transfer them to a wire rack to cool completely.