Preheat the oven to 350°F. Lightly grease (or line with parchment) two baking sheets., Combine the sugars, peanut butter, butter, salt, baking soda, and vanilla, beating until smooth., Add the egg, beating to combine., Stir in the oats and flour, then the milk and chocolate chunks., Drop the dough by the tablespoonful onto the prepared baking sheets, leaving about 1 1/2" between them. A tablespoon cookie scoop works well here., Bake the cookies for about 12 to 14 minutes, until they're a medium golden brown., Remove the cookies from the oven, and transfer them to a rack to cool.