1/2 cup unsalted butter, melted
1/2 cup packed light brown sugar
1/4 cup sugar
1 large egg yolk
1 teaspoon vanilla extract
3/4 cup all-purpose flour
3/4 teaspoon ground cinnamon
1/4 teaspoon ground ginger
a pinch of nutmeg
1/4 teaspoon salt
1 cup oats (5-minute or long cooking)
3/4 cup (packed) finely grated carrots
1/3 cup raisins, optional
Frosting:
4 ounces bar cream cheese, room temperature
2 tablespoons butter, room temperature
2 cups confectioners' sugar
1 - 2 teaspoons heavy cream or milk