Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or lightly grease it.
In a large bowl, whisk together the 1 cup all-purpose flour, 1 cup yellow cornmeal, 2/3 cup granulated sugar, 2 tsp salt, and 2 tsp baking powder until well combined.
1 cup all-purpose flour, 1 cup yellow cornmeal, 2/3 cup granulated sugar, 2 tsp salt, 2 tsp baking powder
In a separate medium bowl, beat the 1 large egg and then mix in the 6 tbsp vegetable oil and 1/2 cup whole milk until well combined.
1 large egg, 6 tbsp vegetable oil
Pour the wet ingredients into the dry ingredients and stir just until combined. Be careful not to overmix.
Gently fold in the blackberries, ensuring they are evenly distributed throughout the batter.
1 cup blackberries
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs.
Allow the muffins to cool in the tin for about 5 minutes, then transfer them to a wire rack to cool completely.