Yield: About 2 dozen
8 eggs, separated
1 cup + ½ cup granulated sugar, divided
1 tablespoon vanilla sugar
½ teaspoon salt
¾ cup oil
1 cup potato starch
2 cups almond flour
½ teaspoon instant
¼ cup hot water
3 tablespoons coffee granules
1 lb. confectioners’ sugar
½ cup chopped walnuts
Prepare the cookies: Preheat oven to 350°F. Line 2 baking sheets with parchment paper and set aside.
In the bowl of an electric mixer fitted with clean beaters (so the egg whites whip up properly), beat the egg whites, adding them one at a time. When they’re frothy, add 1 cup granulated sugar and beat another 2–3 minutes, until peaks form. Transfer to another bowl and set aside.
Add the yolks to the mixer (no need to wash the bowl or the beaters) and beat with the remaining ½ cup sugar for 5 minutes. Add vanilla sugar, salt, and oil and beat to combine. Add the potato starch and beat again.
Remove 2 cups of this mixture and add them to the bowl with the egg whites. (Set aside the rest of the batter for step 6.) Add the almond flour to the egg whites too, and gently fold everything together with a spatula.
Spoon the almond flour mixture into a piping bag or zip-top bag with one corner snipped off. Pipe 2-inch circles onto the prepared baking sheets, leaving at least 1½ inches between cookies.
Add cocoa powder and coffee to the batter that you set aside in step 4. Beat to combine. The mixture will be slightly runny.
Working with one cookie at a time, dip a fork into the mocha mixture and gently swirl it into the top of the cookie, creating a marbled effect (without changing the cookie’s shape). You will need to dip the fork into the mixture separately for each cookie.
Bake for 10–12 minutes, until firm. Set aside to cool before glazing.
Prepare the glaze: In a bowl, mix together the hot water and coffee granules until the coffee is dissolved. Add confectioners’ sugar and whisk to combine, adding a bit more water if it’s too thick. Drizzle over the cookies and top with walnuts.