Heat oven to 350° F.
In a large bowl, combine the flour, oat bran, baking soda, cinnamon, allspice, and salt; set aside.
Beat the butter and sugar in the bowl of an electric mixer on medium-high until smooth. Add the eggs and beat to combine. Add the sour cream and molasses and beat to combine. Slowly add the flour mixture, mixing until incorporated. Fold in the raisins.
Spoon the batter into a muffin tin lined with paper liners. Bake until cooked through and a toothpick inserted in the center of a muffin comes out clean, about 25 minutes.
Serve with butter, if desired.
Make-Ahead Note: You can prepare the batter up to 12 hours in advance. Keep it in the refrigerator until ready to bake.