One-Bowl, No-Mixer, No-Chill Oatmeal Cookies

large egg

unsalted butter (1 stick), very soft

light brown sugar, packed

granulated sugar

vanilla extract

old-fashioned whole rolled oats (not instant or quick cook)

all-purpose flour

baking soda

salt, or to taste

cup semi-sweet chocolate chips, plus more for after baking (or substitute with raisins, walnuts, etc.)