Position a rack in the center of the oven and heat the oven to 350°F. Line a 9x13-inch baking pan with foil, leaving a 2-inch overhang on the ends. Spray the foil with cooking spray. Make the crust and topping In a food processor, finely grind 1/2 cup of the walnuts with the sugar. Add the flour, baking powder, and salt and pulse to blend. Add the butter and pulse until it's the size of small peas, 5 or 6 one-second pulses. Transfer 1 generous cup of the mixture to a medium bowl and set aside. Add the egg to the mixture remaining in the food processor and pulse just until the dough begins to gather into large clumps. With your fingertips, press the dough evenly into the bottom of the prepared pan. Using the tines of a fork, dock the crust all over. Bake until the edges are light goldenbrown and the center looks dry, 15 to 20 minutes. Cool the crust on a rack. Meanwhile, knead the reserved mixture with your fingertips until it becomes clumpy. Coarsely chop the remaining 1/2-cup walnuts and toss them into the mixture; set aside for the topping. Make the filling In a medium saucepan, combine 2 cups of the cranberries with the apples, sugar, maple syrup, apple brandy, and salt. Bring to a simmer over medium heat. Cook, stirring occasionally, until the sugar has dissolved, the cranberries have popped open, and the mixture is thick and syrupy, 4 to 6 minutes. Remove the pan from the heat and stir in the remaining 1 cup cranberries. With a rubber spatula, scrape the cranberry mixture onto the crust and spread evenly. Sprinkle the reserved topping over the cranberry layer, pressing the streusel between your fingers into small lumps as you sprinkle. Bake until the topping is golden, 20 to 25 minutes. Let cool in the pan on a wire rack until just warm, about 1 hour. Carefully lift the bars out of the pan using the foil overhang, peel back the edges of the foil, and cool completely on the rack. Cut into 24 pieces. The bars will keep in an airtight container at room temperature for up to 3 days. nutrition information (per serving): Calories (kcal): 210; Fat (g): 11; Fat Calories (kcal): 100; Saturated Fat (g): 5; Protein (g): 2; Monounsaturated Fat (g): 2.5; Carbohydrates (g): 28; Polyunsaturated Fat (g): 2.5; Sodium (mg): 95; Cholesterol (mg): 30; Fiber (g): 2;