Preheat your oven to 400°F. Line a standard 12-cup muffin tin with paper liners and set aside.
In a large bowl, whisk together the self-rising cornmeal mix, self-rising flour, and sugar until well combined.
In a medium bowl, whisk together the egg, milk, and vegetable oil until smooth and fully combined.
Make a well in the center of the dry ingredients, then pour the wet ingredients into the well. Stir gently until just combined. Be careful not to over-mix.
Gently fold the blueberries into the batter, taking care not to break them apart.
Spoon the batter evenly into the prepared muffin cups, filling each about 2/3 full.
Place the muffin tin in the oven and bake for 20-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and let them cool in the tin for a few minutes. Then, transfer them to a wire rack to cool completely.