Preheat the oven to 400°F (200°C). Lightly grease an 8-inch (20 cm) round baking pan or a 9-inch (23 cm) cast iron skillet. Reserve a small handful of blueberries and 1 teaspoon of the granulated sugar for the top.
Whisk together the flour, cornmeal, sugar, baking powder, baking soda, and kosher salt in a large mixing bowl until evenly combined.
1 cup (125 g) all-purpose flour, 1 cup (150 g) medium-grind yellow cornmeal, ⅓ cup (67 g) granulated sugar, 2 tsps (8 g) baking powder, ½ tsp (2 g) baking soda, ¾ tsp (4 g) kosher salt
In a separate bowl or large measuring jug, whisk together the eggs, buttermilk, melted butter, vegetable oil, lemon zest, lemon juice, and vanilla extract until smooth.
2 large eggs, 1 cup (240 ml) buttermilk, ⅓ cup (75 g) unsalted butter, 2 tbsps (30 ml) vegetable oil, finely grated zest of two lemons, 2 tbsps (30 ml) fresh lemon juice, 1 tsp (5 ml) vanilla extract
Pour the wet ingredients into the dry ingredients and stir just until no dry streaks of flour remain. The batter should look slightly lumpy. Overmixing can produce a tougher cornbread.
Toss the blueberries with the tablespoon of flour until lightly coated, then gently fold them into the batter with a spatula. The flour helps keep the blueberries evenly distributed throughout the cornbread as it bakes.
1½ cups (225 g) fresh blueberries, 1 tbsp (8 g) all-purpose flour
Spread the batter evenly into the prepared pan. Scatter the reserved blueberries over the top and sprinkle with the reserved teaspoon of sugar.
a small handful of fresh blueberries, 1 tsp (8 g) granulated sugar
Bake for 22 to 28 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs attached.
Let the cornbread cool in the pan for at least 15 minutes before slicing and serving. This short cooling time allows the crumb to finish setting for cleaner slices.