Preheat oven to 400 degrees. Coat a 12-hole muffin tin with cooking spray.
In a medium bowl, combine the flour, wheat bran, salt, baking soda, and cinnamon; set aside.
Using an electric mixer, in a large bowl, cream butter with sugar until sugar is dissolved; add egg and beat thoroughly. Add 1/3 of the bran mixture and 1/3 cup of buttermilk; mix until just combined. Repeat, alternating with remaining bran mixture and butermilk. Fold in raisins.
Fill each prepared muffin hole about 2/3 full with batter; place tray in the middle of the oven. Bake until a toothpick inserted into the center of a muffin comes out clean, about 15-20 minutes. Serve warm or cooled.