Instructions

Pan preparation

1. Line a 13" x 9" pan with aluminum foil. I used one sheet that fit lengthwise and then put a second sheet that fit width wise over it (like a plus sign). When you push the two sheets into the pan, the edges line up in the corners with no wrinkles. It's OK if there's a little gap between the edges. You also want a couple of inches of aluminum foil to
   hang over the sides. This makes it easy to remove the marshmallow from the pan.
2. Spray the aluminum foil with cooking spray. Also spray two spatulas with cooking spray.

Oreo layer 1

1. Place gelatin, hot water, and black cocoa powder in the bowl of a stand mixer fitted with a wire whisk. Turn the mixer on low to combine the ingredients. (I leave the mixer on while I'm preparing the syrup).
2. Put the remaining ingredients in a heavy medium-sized saucepan and cook over medium high heat until the sugar syrup reaches 240°F.
3. Turn the mixer up to medium and slowly pour the hot sugar syrup into the bowl. (I pour it along the side to prevent splashing).
4. Turn the mixer to its highest speed and whip the marshmallow until the bowl is just warm to the touch.
5. Work quickly. Use one greased spatula to remove marshmallow from the wire whisk (you won't get all of it). Then use the other greased spatula to scrape the marshmallow out of the bowl as you pour it into the pan. Smooth the top if necessary.
6. Place in the refrigerator while you prepare the vanilla layer.

Vanilla layer

1. Place unflavored gelatin, vanilla and hot water in the clean bowl of a stand mixer fitted with a wire whisk. Turn the mixer on low. If you have marshmallow on your spatulas, you may need to clean them and spray again with cooking spray.
2. Put the remaining ingredients in a heavy medium-sized saucepan and cook over medium high heat until the sugar syrup reaches 240°F.
3. Turn the mixer up to medium and slowly pour the hot sugar syrup into the bowl. (I pour it along the side to prevent splashing).
4. Turn the mixer to its highest speed and whip the marshmallow until the bowl is just warm to the touch.
5. Work quickly. Use one greased spatula to remove marshmallow from the wire whisk (you won't get all of it). Then use the other greased spatula to scrape the marshmallow out of the bowl as you pour it on top of the bottom oreo layer. Smooth the top with a greased spatula if necessary.
6. Put back in the refrigerator while you make the final layer.

Top Oreo layer

1. Repeat the instructions for the bottom oreo layer.
2. Pour on top of the vanilla layer and smooth with a spatula if necessary.

Dusting Powder

1. Combine cornstarch and powdered sugar.
2. Dust the tops of the marshmallows with the powder and let set overnight (this does not require refrigeration).
3. Keep the rest of the powder in a sealed container for dusting the cut marshmallows.

Cutting the marshmallows

1. Remove the marshmallows from the pan and carefully peel away the aluminum foil.
2. Place the marshmallows dusted side down on a cutting board and dust the tops with dusting powder.
3. Use a sharp knife to cut the marshmallows. If the marshmallow sticks to your knife, use a little cooking spray on the knife.
4. I cut my marshmallows into five long strips and then cut each strip into cubes. I find it easiest if you use the extra dusting powder on the cutting board to rub the sides of the long strips after they are cut (so they are no longer sticky) and then to rub the cut ends as I go.