For the pear Helene with homemade chocolate sauce, break the chocolate into coarse pieces. Dissolve them in a water bath. Mix vanilla, hot tap water and whipped cream until a smooth sauce is formed. Keep warm and stir again until smooth before using.
Peel the pears, cut out the core and cut in half. Drizzle with juice of one lemon to prevent them from browning and set aside, covered.
Pour the vanilla ice cream into decorative dessert bowls, place two pear halves on each and pour the warm chocolate sauce over them.
Sprinkle the pear Helene with homemade chocolate sauce with some chopped pistachios and serve.