POSITION rack in centre of oven, then preheat to 350F. Line a large baking sheet with parchment paper.
STIR peanut butter with sugar and egg yolk in a large bowl until smooth.
SCOOP 1 tsp portions and roll each into a ball. Arrange, 1 in. apart, on prepared sheet. Bake until tops are just cracked, 9 to 10 min. Let cookies rest on baking sheet for 5 min, then transfer to a rack to cool completely.
SCOOP 1 tsp melted chocolate into each liner. Press 1 cookie, flat side down, into each cup, pushing some of the chocolate up the side. Scoop another 1 tsp melted chocolate to cover cookie. Let stand until chocolate is firm, about 30 min.
Weekend Baking: Peanut Butter Cookies
Nutrition (per serving)
Kitchen Tip: If you can’t find gold foil liners, use mini paper liners and peel off liners when chocolate is firm. If you’re allergic to peanuts, substitute tahini for peanut butter.
Kitchen Tip: Store in a covered container up to 2 weeks, or freeze up to 1 month.