Line an 8×8-inch square tin with parchment in a criss-cross fashion, allowing a 1-inch overhang on all sides. Spray with nonstick spray.

Pour 120 milliliters (1/2 cup) water into a large mixing bowl (if using a hand mixer), or the bowl of a stand mixer. Sprinkle the gelatin evenly over the water. Set aside.

In a large, heavy-bottomed stock pot, stir together granulated sugar, corn syrup, remaining water, and salt. Bring to a boil and boil, without stirring, until syrup reaches 240° F (116° C) on a candy thermometer.

Carefully pour hot syrup over gelatin. Mix on high speed for 2-3 minutes, or until mixture begins to thicken. Add the vanilla bean paste and continue to mix on high speed until very thick and voluminous, about 8-9 minutes more.

Add crushed Oreos and mix on low speed for 15-30 seconds, or until just barely incorporated.

With an oiled rubber spatula, scrape marshmallow into prepared tin. Loosely cover with a well-oiled sheet of aluminum foil. Allow to set at room temperature until firm, at least 4 hours or overnight.

Cutting and Coating:

Scrape the cream from 12 single-stuffed Oreos. Discard the cream. Blitz cookies in a food processor, or place in a sealed plastic bag and use a rolling pin or mallet to crush. The Oreos should resemble breadcrumbs, although it’s fine if a few larger cookie chunks are still present.

In a small bowl, whisk dry milk powder and Oreo crumbs.

Dust a large chopping board with the powder. Turn marshmallow slab out onto dusted surface. Sift top of slab with more powder.

With a well-oiled knife, cut the slab into squares.**

Toss cut marshmallows in additional powder, coating all sides evenly.

Store in a large ziploc bag or airtight container at room temperature for up to 1 month.