Nonstick cooking spray
3 1/2 cups all-purpose flour (spooned and leveled), plus more for pans
4 teaspoons baking powder
3/4 teaspoon fine salt
3/4 cup (1 1/2 sticks) unsalted butter, room temperature
1/2 cup packed dark-brown sugar
2 large eggs
1 1/2 cups pure maple syrup
3/4 cup whole milk
1 cup chopped walnut halves, toasted
8 ounces cream cheese, room temperature
3/4 cup (1 1/2 sticks) unsalted butter, room temperature
3/4 cup packed dark-brown sugar
2 cups confectioners' sugar