Melt the dark chocolate with a double boiler or microwave. Repeat with the white chocolate. Set both melted chocolates aside to cool, stirring occasionally to prevent them from solidifying.

Place white chocolate, 2 tablespoons ground pistachios and 2 tablespoons heavy cream in a blender. Blend to a smooth cream. Reserve 1 tablespoon of pistachios for garnish.

Using a mixer, beat the remaining cream until fluffy, starting with 30 seconds on the lowest speed. After this time, increase the speed to the highest setting and whip until the cream becomes stiff and the mixer tip leaves clear traces in the cream.

Gently stir one third of the cream into the pistachio mixture, then stir the remaining cream into the dark chocolate. Do not whip or mix for too long, just until all the ingredients are combined.

Prepare 2 glasses. At the bottom of each glass, using a teaspoon, put a chocolate layer, then a pistachio layer. Cover and refrigerate for 1 hour. Garnish with the remaining pistachios just before serving.