Lightly spray a 9-by-13-inch baking pan with oil, line the base and sides with parchment paper (with some overhang on the sides) and lightly spray the paper with oil.
Begin by making the sugar and honey syrup. Combine the 1 ¾ cups sugar, the honey and ½ cup water in a medium, deep heavy-based saucepan. Stir over medium heat until the sugar dissolves.
Bring to a boil and simmer, without stirring, until the syrup reaches 240°F (115°C) on a candy thermometer. Watch it carefully, as the syrup has a tendency to bubble up, and lower the heat a bit if necessary to control it.
Meanwhile, slowly sprinkle the gelatin over the ⅔ cup cold water in a shallow microwave-safe bowl and set aside for 5 minutes. Heat in the microwave for 30 to 45 seconds, or until the gelatin has dissolved.
Once the sugar syrup reaches 240°F (115°C), start whisking the egg whites in an electric mixer with a whisk attachment on medium speed. When frothy, increase the speed to medium-high and gradually add ¼ cup sugar, whisking until thick and glossy. Keep the mixer running on medium speed.
When the sugar syrup reaches 260°F (127°C) (this is the upper end of the hard-ball stage), turn off the heat and allow the bubbles to subside.
Increase the mixer speed to medium-high and gradually pour the gelatin mixture down the inside of the bowl in a thin, steady stream. Add the hot sugar syrup in the same manner. Increase the speed to high and whisk until the mixture is very thick and holds its shape, about 10 to 12 minutes, depending on your mixer. The outside of the bowl should almost be at room temperature.
Meanwhile, put the peanut butter in a small microwave-safe bowl and heat in the microwave for about 15 seconds until softened slightly, but not hot.
Reserve a couple tablespoons of the peanut butter and use a large spoon or spatula to gently fold the rest through the marshmallow mixture, stirring and lifting the mixture only 2 to 3 times. Do not over-mix.
Use the spatula to scrape the marshmallow mixture into the prepared pan and gently smooth it out. Swirl the reserved peanut butter through the top of the marshmallow. Stand at room temperature uncovered for 2 to 3 hours, until set.
Meanwhile, to make the coating, sift the icing sugar and cornstarch together. Dust the top of the marshmallow with some of the coating and turn it out onto a clean surface. Peel away the parchment paper, and dust the bottom with more coating.
Use a large knife sprayed with oil to cut the marshmallow into pieces, cutting rows of 5 by 7 to yield 35 squares. Cut straight down instead of pulling the knife through to get the cleanest cuts. Toss the pieces in the remaining coating, dusting off the excess.
Keep in an airtight container for 2 to 3 days.
If using a natural-style crunchy peanut butter, it may be soft enough at room temperature, in which case you could skip the step to microwave it.
It took me about 20-ish minutes to cook my sugar and honey mixture to the soft ball stage, and another 5-ish minutes before it reached the hard ball stage. I'm not including these timing estimates in the recipe above as they could differ vastly based on your cooking vessel, stovetop temperature, etc., but this is a general guide about how long it could take. Use a candy thermometer for the most accurate results.