Preheat oven to 350°F (177°C) and line a 12-count muffin pan with cupcake liners.
In a large bowl, whisk melted butter, brown sugar, and granulated sugar until smooth.
Add eggs, milk, and vanilla, whisking until fully combined.
In a separate bowl, combine flour, baking soda, baking powder, salt, cinnamon, and nutmeg.
Gradually mix dry ingredients into wet mixture, stirring just until combined.
Fold in the chopped apples gently using a spatula.
Divide batter evenly among cupcake liners (about 3/4 full).
Bake 20–22 minutes, or until a toothpick comes out clean. Let cool completely before frosting.
To make the frosting, melt butter in a saucepan over medium heat. Stir in brown sugar and 2 tablespoons cream. Bring to a gentle boil and simmer for 2 minutes, stirring constantly.
Remove from heat, stir in salt and remaining cream, then let cool for 10–15 minutes.
Transfer to a bowl and beat with confectioners’ sugar until fluffy and spreadable.
Frost cooled cupcakes and top with caramel drizzle or apple slices if desired.