Chocolate Chip Cookie Cake

INGREDIENTS

1 cup

all-purpose flour

1 cup

white whole wheat flour or whole wheat pastry flour

3/4 tsp

baking soda

1/4 tsp

freshly grated nutmeg (optional)

10 tbsp

unsalted butter, softened to room temperature

2/3 cup

packed light brown sugar

1/4 cup

granulated sugar

1 tsp

kosher salt

large egg plus 1 egg yolk, at room temperature

1 tbsp

whole milk*

2 tsp

pure vanilla extract

1 1/4 cups

semisweet chocolate chips

1 1/2 cups

plus 2 tablespoons powdered sugar

1/4 cup

unsweetened cocoa powder

6 tbsp

unsalted butter, softened to room temperature

2 tbsp

whole milk*

1/2 tsp

instant espresso powder (optional—it will intensify the chocolate flavor without making the frosting taste like coffee)

1 tsp

pure vanilla extract

kosher salt, to taste