Prep the pan and oven. Heat your oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment. Grease the parchment too for easy release.

Mix the dry ingredients. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

Cream the butter and sugar. In a large bowl, beat the softened butter and sugar with a hand mixer until pale and fluffy, about 2–3 minutes. This step builds structure and lightness.

Add eggs and flavorings. Beat in the eggs one at a time, mixing well after each. Stir in the vanilla and lemon zest. If the mixture looks slightly curdled, don’t worry— it will smooth out when you add the dry ingredients.

Alternate dry ingredients and buttermilk. Add one-third of the dry mixture, then half the buttermilk. Repeat, ending with the dry mixture. Mix on low just until combined. Do not overmix or the cake can turn tough.

Toss blueberries with flour. In a small bowl, toss the blueberries with 1 tablespoon of flour until coated. Gently fold them into the batter using a spatula, reserving a small handful for the top if you like a pretty finish.

Fill the pan. Spread the batter into the prepared pan. Smooth the top, then scatter on the reserved blueberries. Sprinkle 1–2 tablespoons of sugar evenly over the surface for a crackly crust.

Bake. Bake for 35–45 minutes, or until the top is golden and a toothpick inserted in the center comes out clean or with a few moist crumbs. If using frozen berries, allow a few extra minutes of bake time.

Cool and release. Let the cake cool in the pan for 15 minutes. Run a knife around the edge, invert onto a rack, peel off the parchment, and flip right side up. Cool at least another 30 minutes before slicing.

Serve. Enjoy warm or at room temperature, plain or with a dollop of whipped cream, a spoonful of yogurt, or a light dusting of powdered sugar.