Preheat the oven to 350 degrees.
Spread the peeled and diced apples out on a baking sheet lined with parchment paper and sprinkle the cinnamon on top. Toss to evenly coat the apples with cinnamon. Bake for 10 minutes.
Place 24 cupcake liners in a muffin pan.
Combine cream cheese and butter in a large bowl and beat with a mixer at high speed until thoroughly combined. Add sugar and beat until the batter is fluffy. Add the vanilla and eggs and continue to beat until combined.
In a separate mixing bowl, combine flour, baking powder, baking soda and salt and stir to combine.
With the mixer on low speed, add half of the dry ingredients into the wet ingredients. Next, add the buttermilk and then add the rest of the flour mixture.
Gently fold in the baked, diced apples.
Spoon the muffin batter evenly into the lined muffin cups and place about 1/2 tablespoon chopped nuts on top of each muffin. The nut topping is optional.
Bake for 25 minutes. Cool on a wire rack.
To add an optional vanilla cinnamon glaze drizzle, combine 1/2 cup powdered sugar in a bowl. Add cinnamon to taste. Add 1 tablespoon at a time of milk and mix with a whisk until desired consistency is reached. Add 1/4 teaspoon vanilla extract and mix with a whisk. Drizzle on top of each cooled muffin using a spoon and waving it back and forth on top of the muffin.