Preheat oven to 350°F (180°C).
Combine the first three ingredients in a small bowl and set aside for topping.
Combine buttermilk and wheat bran; let stand. Stir together flour, baking powder, soda and salt; set aside.
Cream together butter and brown sugar. Add egg and vanilla and beat well. Add the dry mixture to the creamed mixture alternately with the buttermilk and bran, mixing well after each addition. Stir in 1 cup (250 mL) diced rhubarb.
Spoon into prepared 9″ x 9″ (2 L) pan. Top with remaining diced rhubarb. Sprinkle this with the almond topping. Bake for 45 – 50 minutes or until done.
*To substitute for 1 cup (250 mL) buttermilk; use 1 tbsp. (15 mL) lemon juice plus enough milk to make 1 cup (250 mL).