Preheat the oven to 350°F (180°C). Line a 12-hole muffin tin with muffin paper liners. Slightly oil with oil spray. Set aside.
In a large mixing bowl, whisk vanilla yogurt, olive oil, sugar, and vanilla if used. If your yogurt is unflavored or your yogurt has a light vanilla flavor, I highly recommend adding the vanilla extract or the muffin are a bit bland.
Fold in self-rising flour and cinnamon (if used), and stir to incorporate until the batter is thick and smooth.
If you want to add fruits, stir in ¾ cup of fresh or frozen blueberries now.
Divide the batter evenly in the prepared pan - it makes 12 small muffins or fill only 10 cups to make bigger muffins.
If you like, press a few frozen blueberries or raspberries on top of each muffin to create a range of flavors.
Bake the muffins at 350°F (180°C) for 22-25 minutes. Check if the muffins are ready by inserting a toothpick in the center. If it comes out clean, it's ready to remove from the oven. If not, bake longer, in 2-minute increments, until the crumb is set.
Let the muffins cool down on a cooling rack before at room temperature for 30 minutes before serving.
