Preheat oven to 400°F (200°C). Line a muffin tin with paper liners.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In another bowl, mix milk, vegetable oil, egg, and vanilla extract.
Pour wet ingredients into dry ingredients and stir until just combined.
Gently fold in the wild blackberries.
Divide the batter evenly among the muffin cups.
Bake for 20 minutes or until a toothpick inserted into the center comes out clean.
Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.