Preparation

Make the crust

• Position a rack in the center of the oven, and heat the oven to 350°F.
• In a large bowl, whisk the cookie crumbs, sugar, flour, and salt. Add the butter, and stir until well combined.
• Press the crumbs into the bottom and side of a 9-inch tart pan with a removable base. Chill the pan in the freezer for 10 minutes, and then put on a large rimmed baking sheet. Bake until the crust is fragrant and set, about 10 minutes. Transfer to a wire rack to cool completely.

Make the fool

• In a medium saucepan, combine the cranberries, maple syrup, and zest. Cook over medium-high heat, stirring occasionally, until the berries pop and the juices thicken, about 10 minutes. Let cool slightly.
• Scrape half of the cranberry mixture into a food processor or blender, and purée until smooth, scraping the bowl as needed. Combine the puréed and unpuréed berries in a medium bowl, cover, and chill until cold.
• In the bowl of a stand mixer fitted with the whisk attachment (or a large bowl and hand-held electric mixer), whip the heavy cream and sour cream on high speed until thick and shiny, scraping down the bowl as needed, about 2 minutes.
• Dollop about one-third of the cream into the cranberry mixture, and fold with a large silicone spatula. Continue adding the cream, one-third at a time and gently folding, until well mixed but with some cranberry streaks remaining.
• Spoon the cranberry mixture into the tart shell. Refrigerate until set, about 2 hours. Sprinkle with the pistachios, then cut into slices and serve.