Preheat your oven to 350°F and line a standard muffin tin with liners.
In a small bowl, combine cinnamon and granulated sugar.
To make the brown sugar swirl, stir together the brown sugar, flour, sea salt, and cinnamon.
Peel, core, and finely chop the apple.
Combine the room temperature eggs along with the cooled melted butter, milk, and vanilla at medium-low speed.