Preheat the oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together flour, granulated sugar, baking powder, salt, and cinnamon.
In a separate bowl, whisk melted butter, milk, eggs, and vanilla extract until smooth.
Fold the wet ingredients into the dry ingredients until just combined; avoid overmixing.
Beat cream cheese with powdered sugar until smooth and creamy.
Fill each muffin liner halfway with batter, add a spoonful of the cream cheese filling, then cover with remaining batter.
Sprinkle the tops with cinnamon sugar.
Bake for 18 to 20 minutes, until golden and a toothpick inserted in the muffin (not the filling) comes out clean.
Cool muffins in the pan for a few minutes, then transfer to a cooling rack to cool completely.
If desired, drizzle cooled muffins with melted white chocolate.