A guaranteed crowd-pleaser, this big, chewy cookie is chock-full of oats, coconut, and chocolate. Cut slices and serve warm with ice cream.
Preheat oven to 350 degrees. Whisk together flour, baking soda, and salt. Beat butter with sugars on medium speed until creamy, about 3 minutes. Beat in egg and vanilla. Beat in flour mixture, then oats, coconut, and chocolate.
Spread mixture evenly into a 10-inch ovenproof nonstick skillet (preferably cast iron). Bake until just set in center and golden around edges, 20 to 25 minutes. Let cool 15 minutes, then serve warm with ice cream.
You can sprinkle an additional two tablespoons of coarsely chopped chocolate, or chocolate chips or disks, on top before baking.