1 ½ cups bran cereal (such as Kellogg’s® All-Bran®)
1 cup all-purpose flour
2 teaspoons cocoa powder
1 teaspoon baking soda
1 teaspoon baking powder
½ teaspoon salt
⅛ teaspoon ground cinnamon
⅛ teaspoon ground cloves
⅔ cup dark brown sugar
⅓ cup vegetable oil
½ teaspoon vanilla extract
¾ cup raisins (Optional)
Preheat oven to 375 degrees F (190 degrees C). Grease 12 muffin cups or line with paper muffin liners.
Stir milk and lemon juice together in a bowl; let sit until milk curdles slightly, about 5 minutes. Pour bran cereal into milk mixture and let cereal soften, about 5 minutes more.
Sift flour, cocoa powder, baking soda, baking powder, salt, cinnamon, and cloves together in a bowl. Beat brown sugar, vegetable oil, egg, and vanilla extract together in another bowl. Stir egg mixture into flour mixture until batter is just-combined.
Stir bran cereal mixture into batter; fold in raisins. Spoon batter into prepared muffin cups.
Bake in the preheated oven until browned and set, 16 to 18 minutes.