Marshmallow Slab:

Line an 8×8-inch / 20 x 20-centimeter square tin with parchment, and coat generously with oil. (See this recipe for the best lining technique!) Set aside until ready to use.

Pour 105 milliliters (1/2 cup) water into a large mixing bowl (if using a hand mixer), or the bowl of a stand mixer. Sprinkle the gelatine evenly over the water, and set bowl aside.

Combine sugar, corn syrup, remaining water, and salt in a large saucepan. Bring mixture to a boil and boil, without stirring, until syrup reaches 240° F / 116° C on a candy thermometer.

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

Add 140 grams crushed Oreos and mix on low for 15-30 seconds, just long enough to incorporate them into the mixture.

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

Cutting and Coating:

Remove cream portion from 100 grams Oreos (about 12 sandwich cookies). Blitz in a food processor, or place cookies 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, combine the dry milk powder** and crushed Oreos.

Cover a large chopping board with a sheet of parchment, and dust generously with milk-and-cookies mixture.

Turn marshmallow slab out onto dusted surface. Sift top of slab with more of the powdered milk and cookies.

Use a well-oiled knife to cut the slab into squares. I usually cut 4 rows x 4 rows for oversized marshmallows, or 6 rows x 6 rows for smaller marshmallows. If desired, you can also use a metal cutter to cut your marshmallow slab into shapes, such as hearts, stars, or circles, instead.

Toss cut marshmallows in additional cookies-and-cream mixture, making sure all sides are evenly coated in the powder.

Marshmallows will keep well for several weeks when stored in an airtight container at room temperature.