How to Make It
Make the marshmallows Coat a 13-by-18-inch rimmed baking sheet with cooking spray. Line with parchment paper and coat with cooking spray. In a small microwavable bowl, whisk the gelatin with 3/4 cup of water. Microwave on high in 10-second increments, stirring after each one, until the gelatin is just melted, about 50 seconds.
In a stand mixer fitted with the whisk, beat the egg whites at medium-low speed until very foamy. Meanwhile, in a medium saucepan, combine the sugar with the corn syrup and 1 cup of water and bring to a boil, stirring occasionally. Cook over moderate heat, without stirring, until the sugar syrup registers 260° on a candy thermometer, about 10 minutes. Remove the pan from the heat and carefully stir in the gelatin until melted.
Carefully drizzle the hot syrup into the egg whites down the side of the bowl, beating at medium speed. Add the vanilla and beat at high speed until thick and glossy, about 10 minutes. Using a rubber spatula, fold in the 1 cup of peppermint candies. Sprinkle in the food coloring, then quickly scrape the marshmallow mixture onto the prepared baking sheet, swirling the food coloring, and smooth the surface. Let stand at room temperature until set, at least 2 hours or overnight.
Meanwhile, make the cookies In a medium bowl, whisk the bread flour with the pastry flour and salt. In a stand mixer fitted with the paddle, beat the butter with the sugar and vanilla bean seeds at medium speed until fluffy, about 5 minutes. Beat in the egg, egg yolk and vanilla extract. Beat in the dry ingredients at low speed until just combined. Divide the dough in half and press into disks. Wrap in plastic and refrigerate until firm, at least 1 hour or overnight.
On a lightly floured sheet of parchment paper, roll out 1 disk of dough into a rectangle, 1/4 inch thick. Transfer on the parchment paper to a baking sheet and refrigerate until firm, about 30 minutes. Repeat with the second disk of dough.
Preheat the oven to 325°. Using a square cookie cutter or a knife, cut 2-inch squares from the dough and arrange on the baking sheets 1 inch apart. Reroll the scraps and cut more squares. Bake the cookies for 10 to 12 minutes, until golden brown. Transfer the baking sheets to wire racks and let the cookies cool.
Lightly brush the cookie cutter or a knife with oil, repeating as needed. Cut out forty-eight 2-inch marshmallows. Place 1 marshmallow on top of each cookie and transfer to baking sheets. Freeze until cold, at least 15 minutes.
Make the glaze In a large microwavable bowl, combine the chocolate with the cocoa butter. Microwave on high in 20-second increments, stirring after each one, until the mixture is melted and smooth.
Coat 2 rimmed baking sheets with cooking spray. Line with parchment paper and coat with cooking spray. Using a fork, dip each cookie in the glaze, then set on a prepared baking sheet and sprinkle with some peppermint candy. Refrigerate until set, at least 15 minutes, and serve cold.