Preheat oven to 400°F. Lightly spray a muffin top pan with nonstick spray, or line a large sheet pan with parchment paper.
Make the crumb topping. Add flour, sugar, cold cubed butter, and a tiny pinch of salt to a medium bowl. Use your fingers to rub the butter into the flour and sugar until you have a crumbly topping with some small crumbs and a few larger pieces. Place in the refrigerator while you make the batter.
In a large mixing bowl, whisk together Greek yogurt, egg, and vanilla until smooth.
Add the granulated sugar, baking powder, baking soda, and kosher salt. Whisk well until fully combined.
Add the all-purpose flour and use a silicone spatula to fold it in until the batter is about halfway mixed. You should still see some dry streaks of flour.
Continue folding the batter while slowly drizzling in the melted and cooled butter.
When the butter is almost fully mixed in, add the blueberries. Fold just until the blueberries are evenly distributed, the last of the dry ingredients disappears, and the butter is fully incorporated. Do not overmix. The batter will be thick.
Use a medium scoop or two spoons to portion the batter into the prepared muffin top pan, or scoop onto a large sheet pan lined with parchment paper. If using parchment paper, leave a few inches between each mound.
Place a ring mold or mason jar ring around one mound of batter. Sprinkle crumb topping inside the ring so it stays mostly on top of the muffin batter. Lift the ring straight up and repeat with the remaining muffin tops.
Bake at 400°F for 15 to 18 minutes, or until the muffin tops are puffed, lightly golden on the edges, and a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let cool in the pan or on the sheet pan for 10 minutes, then transfer to a wire rack. Serve warm or at room temperature.