Special equipment: Special equipment: Ice-cream maker
Bring 1 cup of the cream and the milk to a simmer in a heavy medium saucepan.
Puree the cucumber in a blender or food processor (or juicer if available), and then strain the juice through a fine sieve until you have 3/4 cup cucumber juice.
Combine the sugar, cilantro and mint in a food processor and process until the herbs are finely ground.
Whisk the yolks with the herb sugar in a heatproof bowl until combined. Gradually whisk in the hot cream mixture until blended, tempering the egg yolks. Return the mixture to the saucepan and add the salt. Stir over medium-low heat (do not boil) until the custard thickens slightly and coats the back of a spoon or an instant-read thermometer inserted into the mixture registers 170 degrees F, about 3 minutes.
Pour the custard through a strainer into a medium bowl set over a slightly larger bowl filled halfway with equal parts ice and cold water.
Stir the mixture until the custard is cool to the touch, about 5 minutes. Remove the bowl from the ice water and whisk in the cucumber juice and yogurt. Refrigerate until well chilled, and then transfer to the ice-cream maker and process according to manufacturer's instructions. Cover and freeze in a freezer container until firm. Serve with the Indian Pistachio Brittle.