Before starting, let the eggs and buttermilk stand for about 30 minutes. Melt the butter and let it cool. Dry fresh berries thoroughly, or keep frozen berries frozen. Grease the flat surface around the muffin cups. Line the tin, then whisk the flour, baking powder, baking soda, and salt in a large bowl until evenly combined. The mixture should look pale and fluffy with no clumps.

Whisk the eggs, both sugars, oil, and melted butter in a second bowl for 1 minute, until thick and glossy. Whisk in the buttermilk, vanilla, and lemon zest until smooth.

Pour the wet mixture into the dry and fold with a spatula for 12 to 15 strokes, until a few small streaks of flour remain.

Toss the blueberries with 1 tablespoon of flour, then fold them in with 5 or 6 gentle strokes. Rest the batter for 20 minutes, until it looks thick and puffed with small bubbles, and preheat the oven to 425°F (220°C) during the last 15 minutes.

Rub the topping flour, sugar, cinnamon, salt, and cold butter together with your fingertips until it forms pea sized crumbs. Scoop the batter into the liners, filling each to the very top, then sprinkle the topping over each one.

Bake at 425°F for 5 minutes, then reduce the oven to 350°F (175°C) without opening the door, and bake 15 to 18 minutes more. The muffins are done when the domes are deep golden and a toothpick comes out clean, with perhaps a smear of berry.

Rest the muffins in the tin for 5 minutes, then slide a thin knife around each dome and move them to a wire rack for 10 minutes. They should feel warm, not hot, when you bite in.