Preheat your oven to 425°F (220°C). Line a 6-count jumbo muffin tin with paper liners.

In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside. (Note: Remove 1 tablespoon of this flour mixture and toss it with the blueberries in a small bowl to prevent them from sinking later).

In a separate medium bowl, vigorously whisk the melted butter, granulated sugar, and lemon zest together until pale and fragrant. Beat in the eggs one at a time, followed by the vanilla extract and buttermilk. Mix until just combined.

Pour the wet ingredients into the dry ingredients. Use a spatula to gently fold them together until *just* combined. Do not overmix; a few lumps are perfectly fine.

Gently fold in the flour-tossed blueberries.

Divide the thick batter evenly among the 6 jumbo muffin cups. They will be very full, mounded all the way to the top.

In a tiny bowl, rub the turbinado sugar and remaining 1 tsp lemon zest together with your fingers until fragrant. Sprinkle this generously over the top of each muffin.

Bake at 425°F (220°C) for 5 minutes. Then, keeping the muffins in the oven, reduce the oven temperature to 375°F (190°C) and bake for an additional 18-22 minutes until a toothpick inserted into the center comes out clean.

Let the muffins cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.