Steps
- Simmer 2 cups of blackberries, ½ cup of sugar, and 1 tablespoon of fresh lemon juice in a saucepan, mashing the berries, for 10 minutes.
- Strain through a fine sieve, pressing the pulp through and scraping the underside. Cool the purée completely over an ice bath, until slightly thickened.
- Whisk the purée with 1 room-temperature pasteurized egg white on high for 8-10 minutes, or until stiff peaks form.
- Meanwhile, bring ⅓ cup of water, 2 teaspoons of agar agar powder, and 1 cup of sugar to a boil over medium heat. Boil gently for 5 minutes, whisking, until thick and flowing in a steady stream.
- Immediately pour the hot syrup slowly into the fruit mixture on the lowest mixer speed, avoiding the whisk and bowl sides. Scrape the bowl, then beat on high for 2-3 minutes, until stiff.
- Immediately pipe similar-sized rosettes through a large open-star tip onto parchment. Leave uncovered at about 70°F / 21°C, away from drafts and humidity, for 6-12 hours, until firm.
- Lift from the parchment, press pairs together at their flat bases, and lightly coat with icing sugar.