Preheat your oven to 350°F (175°C). Butter a 9-inch springform pan. In a food processor, combine raw walnuts, flour, salt, and granulated sugar, pulsing until finely ground. Add cold butter and pulse until the mixture resembles coarse crumbs. Gradually incorporate cold water until the dough comes together. Press the dough evenly into the pan, chill for 20 minutes, then bake for 15-20 minutes until lightly golden and set.

In a medium saucepan, mix granulated sugar, water, and cream of tartar over medium heat. Stir gently until the mixture begins to bubble, then stop stirring and swirl the pan occasionally for about 8-10 minutes. Once the sugar turns a deep amber color, remove from heat and carefully whisk in heavy whipping cream to create a smooth caramel. Allow it to cool slightly before using in the filling.

In a large mixing bowl, whisk together the canned pumpkin puree, light brown sugar, flour, eggs, and the warming spices: cinnamon, nutmeg, ginger, and cloves. Once well combined, pour in the cooled caramel from Step 2 and blend until the mixture is perfectly smooth and creamy.

Gently pour the pumpkin filling into the baked walnut crust, smoothing it out with a spatula. Place the tart in the oven and bake for approximately 35 minutes, or until the filling is set and doesn't jiggle in the center. Once baked, remove the tart from the oven and let it cool on a wire rack.

In a small saucepan over medium heat, combine granulated sugar and water. Stir until the sugar dissolves, then add raw walnuts. Continue cooking, stirring until the mixture turns golden and caramelizes, about 5-7 minutes. Quickly transfer the walnuts onto a parchment-lined baking sheet to cool completely.

Once the tart has cooled, sprinkle the chopped candied walnuts generously on top, creating a beautiful presentation. Allow the tart to chill in the refrigerator for at least an hour before serving.