8ouncesbittersweet or semisweet chocolate, cut into 30 squares
15large marshmallows, halved horizontally
Instructions
Preheat oven to 350 degrees. Line two baking sheets with parchment paper; set aside. In a food processor, pulse oats until finely ground. Add flours, cinnamon, baking soda, and salt; pulse to combine.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar until light and fluffy. Beat in egg; Scrape down the sides of the bowl with a rubber spatula as needed. With mixer on low, beat in flour mixture just until combined.
Roll a heaping tablespoon of dough into a 1½-inch ball and place on prepared baking sheets, 1 inch apart. Butter the bottom of a drinking glass and then dip the bottom of the glass in sugar. Flatten the dough balls with the bottom of the glass until they are about ¾ inch thick, dipping the glass in sugar as necessary to prevent sticking (after every 2 or 3 cookies). Top each with a chocolate square.
Bake just until lightly golden, 11 to 13 minutes, rotating sheets halfway through.
Remove sheets from oven; heat broiler. Top each cookie with a marshmallow. One sheet at a time, broil until marshmallows are lightly browned, 1 to 1 1/2 minutes. Transfer cookies to wire racks to cool.