Pistachio Chocolate Cheesecake

Preheat the oven to 325 degrees Fahrenheit, or 165 degrees Celsius. \nSpray a 9-inch springform pan with cooking spray to prevent the cheesecake from sticking. \nUsing a food processor, grind cookies, 1/4 cup pistachios, and 2 tablespoons sugar into a coarse mixture. \nAdd melted butter to the processor and blend until combined. Spread this mixture evenly into the prepared pan and press it firmly into the bottom of the pan. \nTo make pistachio butter, blend remaining 1/2 cup pistachios in a small food processor until it reaches a smooth consistency. \nTransfer the pistachio butter to a large bowl and add cream cheese, avocado, 1 cup yogurt, cornstarch, and 3/4 cup white sugar. \nBeat the mixture with an electric mixer at medium speed until it's nearly smooth. Add egg whites, almond extract, and a pinch of salt; beat until just combined. \nSpread the mixture over the prepared crust and bake in the preheated oven until the surface near edges appears set when gently wiggled, about 40 minutes. \nTurn off the oven and let the cheesecake stand in it for 30 minutes to allow it to set. \nRemove the cheesecake from the pan and cool it on a wire rack for 15 minutes. \nUsing a thin metal spatula, loosen the cheesecake from the sides of the pan. \nCool the cheesecake completely before serving.

For mousse, beat whipping cream, powdered sugar, vanilla, remaining 1 cup yogurt and a pinch salt in a bowl with an electric mixer at medium-low speed until fluffy, about 4 minutes. \nSpread the mousse over the cooled cheesecake. \nCover the top of the cheesecake with whipped topping and chill, covered, at least 4 hours or up to 5 days. \nTo serve, remove the cheesecake from the pan and slice it. Garnish with additional whipped topping and pistachios.