Directions

1. Combine the butter and sugar and beat on medium speed until well creamed together. Add the egg and vanilla extract. Mix into butter and sugar until the egg is well beaten.
   
2. In a separate bowl, combine flour, cinnamon, baking soda and cream of tartar. Slowly add into dough and beat on medium low speed until well combined and dough starts to form.
   
3. Next fold in the crushed cereal and mini marshmallows and mix to combine. Refrigerate the dough overnight.
   
4. Preheat the oven to 350° F. Use a large cookie scoop (3 tbsp.) and scoop cookie dough onto a parchment paper lined baking sheet, making 12 cookies. Place about 2 inches apart and bake for 15 minutes.
   
5. Allow cookie to cool on the baking sheet for 5 minutes and then transfer to a wire rack to cool completely. If the cookies are really misshaped, you can fix them right when they come out of the oven. Use the flat edge of your knife and push the edges of the cookie back into the center.