Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper.
In a small bowl, mix cream cheese, sugar, sour cream, egg yolk, and vanilla until smooth. Set aside.
In a large bowl, whisk melted butter and light brown sugar until smooth.
Add egg and vanilla extract and mix until combined.
Stir in flour, baking powder, cinnamon, nutmeg, and salt until just combined.
Fold in grated carrots, shredded coconut and nuts (if using).
Spread blondie batter evenly into the prepared pan reserving a few tablespoons for the top.
Spoon cream cheese mixture over the batter. Place dollops of the reserved batter on top.
Use a knife or toothpick to gently swirl the cream cheese into the batter.
Bake for 25–30 minutes, until edges are set and the center is just slightly soft.
Cool completely before slicing.
