Tip:Overfilling the muffin cups gives you those great big bakery-style muffin tops.
Position a rack in the center of the oven and heat the oven to 350°F. Lightly oil (or spray with cooking spray) the top of a standard 12-cup muffin tin and then line with paper or foil baking cups. (Spraying the pan keeps the muffin tops from sticking to the pan’s surface.)
In a large bowl, sift together the flour, baking powder, baking soda, and salt; mix well. In a medium bowl, whisk the sugar, butter, milk, crème fraîche or sour cream, eggs, egg yolk, and zest until well combined.
Pour the wet ingredients into the dry and fold gently with a rubber spatula just until the dry ingredients are mostly moistened; the batter will be lumpy, and there should still be quite a few streaks of dry flour. Sprinkle the blueberries on the batter and fold them in until just combined. (The batter will still be lumpy; don’t try to smooth it out or you’ll overmix.)
If you have an ice cream scoop with a “sweeper” in it, use it to fill the muffin cups. Otherwise, use two spoons to spoon the batter in, distributing all of the batter evenly. The batter should mound higher than the rim of the cups by about 3/4 inch.
Bake until the muffins are golden brown and spring back lightly when you press the middle, 30 to 35 minutes. (The muffin tops will probably meld together.) Let the muffin tin cool on a rack for 15 to 20 minutes. Use a table knife to separate the tops, and then invert the pan and pop out the muffins.