“Fair warning: Once you know how easy it is to make a single peanut butter and chocolate cookie, you might get in the habit of making one every single night. I originally developed this with almond butter, which tastes equally delicious but can be pricey. If you have a peanut allergy, any other nut butter swaps in perfectly well.” —Lindsay Maitland Hunt
Stir the peanut butter, oats, sugar, and vanilla together in a small bowl until completely combined. Using your fingers, shape the mixture into a 2 1/2-inch-wide (6-cm), 1/2-inch-thick (12-mm) disk. Press the tines of a fork into the top of the cookie. Chill on a parchment-lined plate in the freezer until firm, about 5 minutes.
Once the cookie is cold and hard, melt the chocolate in the microwave in 15-second bursts until stirrable. Spread half the chilled cookie with the chocolate, and sprinkle with a little flaky sea salt, if you like. The chocolate should set when it hits the cold cookie, but if it doesn’t, you can return it to the freezer for a minute or two.