Spray a 9-by-12-inch pan with cooking spray, then place a layer of parchment paper cut to size on top. Spray the top of the parchment so it is coated lightly.
Pour 1/2 cup cold water in a small microwave-safe bowl, sprinkle the gelatin powder on top and stir well. Let stand for at least 3 minutes to allow the gelatin to absorb the water.
Combine the granulated sugar, corn syrup, honey and 1/3 cup water in a small saucepan and heat to 250 degrees F. The syrup will thicken and be boiling. Pour the syrup into the bowl of a stand mixer and let stand to cool down to 212 degrees F; this happens fairly quickly.
Microwave the gelatin mixture for 30 seconds to a minute or until the gelatin is completely melted but not over 135 degrees F.
Add the melted gelatin mixture to the cooked syrup. Place the bowl on the mixer with a whip attachment and whip on high, stopping after about 7 minutes to add the vanilla, until the mixture gets white and fluffy, 8 to 10 minutes. Fold in 1 1/2 cups of the crushed Oreos®. Scrape the mixture out into the prepared pan and spread evenly. Top with the remaining 2 cups of crushed Oreos®. Set aside to allow the marshmallows to set up, a couple of hours.
Cut the marshmallows and toss in a 50/50 cornstarch-confectioners' sugar mixture to prevent them from sticking back together. Store in an airtight container at room temperature.