Frozen Coffee Parfaits

Combine 200 ml of water with the sugar and a few drops of lemon juice. Bring to a boil and simmer until reduced by half. Remove from heat and allow to cool slightly. Whisk the egg yolks in a cold, stainless steel bowl until light and frothy. Slowly stream in about 1/3 of the warm sugar syrup into the egg yolks while whisking vigorously. Pour the egg yolks into the saucepan with the remaining syrup and heat on low until thickened. Transfer the mixture to a bowl over an ice bath to chill quickly. Chop the pistachios. Beat the whipping cream with 2-3 tablespoons of espresso until stiff. Stir the remaining espresso into the egg yolk mixture, then fold in the whipped cream and pistachios. Pour the mixture into the cone-shaped molds and freeze for at least 8 hours.