How to Make It
Lightly grease a 9-by-13-inch metal baking pan with canola oil. In a stand mixer fitted with the whisk attachment, beat the corn syrup with the peppermint extract and vanilla seeds at low speed until combined. Reserve the vanilla bean pod for another use.
In a heatproof medium bowl, cover the gelatin sheets with the ice water and let stand, stirring occasionally, until the gelatin is evenly moistened and all of the water is absorbed, about 5 minutes. In a medium saucepan, bring 2 inches of water to a simmer. Set the bowl with the gelatin over the simmering water and cook, stirring once or twice, until melted, about 5 minutes. Do not let the bowl touch the water. Carefully remove the saucepan from the heat.
In a small, heavy-bottomed saucepan, bring the granulated sugar and water to a boil. Cook, without stirring, until the sugar syrup registers 225° on a candy thermometer, 8 to 10 minutes. Use a wet pastry brush to wash down the side of the pan.
With the stand mixer at low speed, slowly stream the hot sugar syrup into the corn syrup. Add the warm gelatin and continue beating until slightly thickened and opaque, about 2 minutes. Increase the speed to moderately high and beat until the marshmallow is thick and glossy and registers 105°, about 12 minutes.
Lightly grease a rubber spatula. Scatter the food coloring over the marshmallow, then, using the spatula, quickly scrape the marshmallow into the prepared pan, swirling the food coloring as you go. Let stand at room temperature until set, at least 3 hours or overnight.
Sift the confectioners’ sugar and cornstarch into a shallow bowl. Invert the marshmallows onto a work surface and cut into 2-inch squares. Toss in the sugar mixture, shaking off any excess, then serve.