Marshmallows:

Line an 8 x 8-inch square tin with parchment, allowing a 1-inch overhang on all sides. Spray generously with nonstick spray. Set aside.

Pour 120 milliliters coffee into a large mixing bowl (if using a hand mixer), or the bowl of a stand mixer. Sprinkle the powdered gelatin evenly over the coffee. Set aside.

In a large, heavy-bottomed stock pot, combine granulated sugar, corn syrup, remaining coffee, and fine sea salt. Bring to a boil and boil, without stirring, until syrup reaches 240° F (116° C) on a digital thermometer.

Carefully pour hot syrup over gelatin. Mix on high speed for 2-3 minutes, until mixture begins to thicken.

Add coffee extract and continue to mix on high speed until very thick and voluminous, about 8-9 minutes more.

With an oiled rubber spatula, scrape marshmallow 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:

In a small bowl, whisk together confectioner’s sugar and potato starch. Dust a large chopping board with the powder. Turn marshmallow slab out onto dusted surface. Sift top of slab with more of the potato starch mixture.

With a sharp, well-oiled chef’s knife, cut the slab into squares.

Toss cut marshmallows in additional potato starch mixture, coating all sides evenly.

Store coffee marshmallows in an airtight container at room temperature for up to 1 month.