Preheat oven to 350 degrees F (175 degrees C). Lightly grease a muffin pan or line with muffin cups.
Combine bran flakes and bran cereal in a heat-proof bowl. Cover with boiling water; stir and let sit until softened.
Beat sugar, shortening, and eggs together in a very large bowl with an electric mixer until creamy.
Sift flour, baking soda, and salt into a bowl. Add flour mixture and buttermilk alternately to sugar mixture. Stir in softened bran; mix until evenly incorporated.
Spoon batter evenly into prepared muffin pan.
Bake in the preheated oven until tops spring back when lightly pressed, about 15 minutes.
