01 -  Preheat oven to 350°F. Lightly grease a mini muffin tin or line with mini paper liners. 
 02 -  Combine diced apple, brown sugar, and ground cinnamon in a small bowl. Set aside. 
 03 -  In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, ground cinnamon, and salt. 
 04 -  In a separate bowl, whisk the egg, milk, melted butter, and vanilla extract until fully blended. 
 05 -  Pour wet ingredients into the dry ingredients and gently mix until just incorporated. Avoid over-mixing. 
 06 -  Carefully fold in the prepared apple mixture, mini marshmallows, chocolate chips, caramel pieces, and graham cracker crumbs until evenly distributed. 
 07 -  Spoon the batter into the wells of the prepared mini muffin tin, filling each about three-quarters full. 
 08 -  Place tin in the oven and bake for 14 to 16 minutes until golden and a toothpick inserted in the center emerges clean. 
 09 -  Remove tin from oven, allowing muffin balls to cool for 5 minutes in the pan. 
 10 -  While still warm, brush muffin tops with melted butter, sprinkle with graham cracker crumbs, and add optional mini chocolate chips and mini marshmallows. 
 11 -  Serve warm or at room temperature as desired.