2. In a saucepan, melt 1 tablespoon of the butter over medium heat. Add the pistachios and 2 tablespoons of the sugar. Heat, stirring often, until the pistachios are coated and the sugar is caramelized. Turn out onto a foil-lined baking sheet and set aside to cool.
3. Melt the remaining butter. In a bowl, mix the cracker crumbs, the remaining 2 tablespoons of sugar, and the melted butter. Press the mixture on the bottom and up the sides of a 9-inch springform pan. Bake 10 minutes. Set aside to cool.
4. In a large bowl of an electric mixer, beat the cream cheese and the brown sugar until light. Beat in the eggs, one at a time, beating well after each addition. Add the sour cream, vanilla, and the caramelized pistachios, breaking them into small pieces, if necessary. Mix to blend thoroughly. Pour the mixture into the prepared crust and bake for 1 hour, or until the edges of the cheesecake are firm but the center is still soft and shiny. Cool completely on a wire rack.
5. For the topping, beat the cream cheese and brown sugar until light. Fold in the whipped cream. Spread the topping over the cooled cheesecake and chill for at least 4 hours.