In a small bowl, combine buttermilk* and bran; set aside. In a large bowl, mix together flour and baking powder.
In a medium bowl, combine oil, egg, sugar and vanilla. Add bran mixture to sugar mixture and mix.
Pour wet ingredients into dry. Add blueberries and mix until just combined.
Spoon batter into a lightly greased 12-muffin tray, filling cups to three-quarters full. Bake at 375°F (190°C) for 15-18 minutes, until a cake tester inserted into the middle of a muffin comes out clean.
*To make a buttermilk substitute, combine 1 cup (250 mL) skim milk with 1 tbsp (15 mL) vinegar; let sit for five minutes.