• In a large heatproof bowl set over a saucepan of boiling water,
combine the eggs, egg yolks, vanilla-bean seeds, and sugar.
Cook, whisking constantly, until frothy, 5 to 6 minutes. Remove
from heat. Using an electric mixer at medium-high speed, beat
until soft peaks form. Set aside.
• In a medium bowl, combine 2 packages blackberries, lemon zest,
and lemon juice. With a fork, lightly mash the berries. Fold the
berry mixture into the egg mixture. Set aside.
• In a large bowl and using an electric mixer at high speed, whip
the cream until soft peaks form. Gently fold the whipped cream
into the egg-berry mixture. Set aside.
• Line a 9-x-9-x-2-inch baking dish with plastic wrap, allowing
wrap to hang over by 2 inches on each end. Scatter remaining
blackberries in prepared dish. Pour whipped-cream mixture
over blackberries. Cover with foil, and freeze overnight.
• Using plastic wrap as handles, lift frozen semifreddo from pan.
Remove plastic wrap. Cut semifreddo into 24 (1 1/2-inch) squares.
• Garnish with fresh blackberries and fresh mint, if desired.
*Superfine sugar can be made by pulsing granulated sugar in a food