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1
Lightly coat an 8-by-8-inch baking pan with cooking spray.
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2
Whisk together the gelatin and cold water in a small bowl, and let it soften for 5 minutes.
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3
Make the chocolate malt syrup. In the bowl of an electric mixer, whisk together the cocoa powder, malted milk powder, hot water, and corn syrup until smooth. Put the bowl on the mixer and fit it with the whisk attachment.
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4
Stir together the sugar, corn syrup, water, and salt in a medium saucepan over high heat. Boil, stirring occasionally, until the temperature reaches 248u00b0F to 250u00b0F. Meanwhile, microwave the gelatin on high until completely melted, about 30 seconds, and pour it into the chocolate syrup. Set the mixer to low and keep it running while you check the sugar syrup.
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5
When the syrup reaches 248u00b0F to 250u00b0F, slowly pour it into the mixer bowl. Increase the speed to medium and beat for 5 minutes. Increase to medium-high and beat for 5 more minutes. Increase to the highest setting and beat for 3 to 5 minutes more, adding the vanilla in the last minute. The finished marshmallow will be tripled in volume. Pour it into the prepared pan, using an offset spatula to smooth it into the corners. Sprinkle grated chocolate evenly and generously over top. Let set for about 6 hours.
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6
Use a knife to loosen the marshmallow from the edges of the pan and invert the slab onto a work surface. Sprinkle it with grated chocolate. Cut it into pieces and dip the sticky edges in more chocolate, patting off the excess.
