Preheat the oven to 180°C (gas mark5). Grease a muffin tin with 6 cups with a bit of margarine and set aside.
In a large mixing bowl, sift together the flour, baking powder and salt. Set aside.
In a medium bowl, mix the soy milk, sugar, oil and vanilla extract together until well combined. Add in the sifted flour mixture and mix until just combined, careful not to overmix!
Fold in the frozen blueberries and gently mix into the batter.
Fill each muffin cup with batter. I fill the batter very near to the top so the muffins came out in the mushroom kind of shape but if you want an ordinary muffin shape, you should fill each cup 2/3 with the batter.
Top each muffin with a few blueberries, maybe 3 or 4. Place in the oven and bake for 30 minutes or a toothpick inserted in the middle of a muffin comes out clean.
Let it cool completely before serving.