Preheat the oven to 425ºF with the cast iron skillet inside, so it can preheat with the oven.

In a large bowl, stir together the cornmeal, flour, sugar, baking powder, and salt.

In a separate bowl, whisk together the milk, oil, egg, and lemon juice.

Mix the blueberries into the dry ingredients, being sure to coat them thoroughly in the dry mix.

Pour the whisked wet ingredients into the bowl with the dry ingredients. Stir just until the dry mixture is completely moistened. A few lumps are okay.

Carefully remove the hot skillet from the oven. Add 1 Tbsp butter to the hot skillet and swirl to spread the melted butter up the sides of the skillet.

Pour the prepared cornbread batter into the hot skillet. Carefully return the skillet to the hot oven. Bake the cornbread for 20-25 minutes, checking at the 18-minute mark. It is ready when the top and sides are deep golden brown and a toothpick inserted into the center comes out clean. Cool slightly, then slice and consume with gusto!