Preheat the oven to 390°F (200°C). Line a standard 12-cup muffin pan with paper liners.
Add the flour, baking powder, baking soda, sugar, and salt to a large mixing bowl. Whisk until evenly combined.
In a separate bowl, whisk together the buttermilk, melted butter, vegetable oil, lightly beaten eggs, and vanilla.
Make a well in the center of the dry ingredients and pour in the wet mixture.
Gently fold the ingredients together just until combined. Avoid excessive mixing; a few small flour lumps are perfectly fine.
Reserve a small handful of blueberries for decorating the tops. Gently fold the remaining blueberries into the batter.
Divide the Blueberry Muffins (Ultra Moist!) batter evenly among the 12 prepared muffin cups.
Scatter the reserved blueberries over the top of each muffin.
Bake at 390°F (200°C) for 5 minutes.
Without opening the oven door unnecessarily, reduce the temperature to 350°F (180°C).
Continue baking for approximately 13 minutes in a fan/convection oven or about 15 minutes in a conventional oven. The muffins are ready when the tops are golden and a skewer inserted into the center comes out clean or with a few moist crumbs.
Remove the muffins from the pan immediately and transfer them to a wire cooling rack.
Serve warm or allow them to cool completely.