Fudgy Oatmeal Chocolate Chip Cookie Bars

unsalted butter (1 stick), melted

large egg

light brown sugar, packed

vanilla extract

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

cup all-purpose flour

salt, optional and to taste

semi-sweet chocolate chips, for batter

half of one 14-ounce can sweetened condensed milk (just eyeball it)

about 1/3 cup semi-sweet chocolate chips, for sprinkling