Preheat oven to 350 degrees. Line muffin cups with muffin papers or lightly spray with nonstick cooking spray. Set aside.
In a small bowl, combine flour, baking powder, salt and cinnamon. Set aside.
With an electric mixer, cream together butter and sugar until smooth. Add eggs, one at a time. Stir in vanilla extract. Stir in 1/2 of flour mixture. Add 1/2 of buttermilk and then the remaining flour mixture. Add in remaining buttermilk and 1 cup muesli.
Divide batter between muffins cups. Sprinkle tops with remaining 1/4 cup muesli. Bake in preheated oven for 30 minutes. A toothpick should come out clean when inserted into the center of the muffin when done. Let cool.