Preheat & prepare the pan: Preheat your oven to 350 °F (≈ 175 °C). Lightly butter a 9‑inch springform or tart pan.

Make the crust: In a food processor add the walnuts, flour, salt, and sugar, pulse until walnuts are finely ground. Add the cold butter and pulse until only small bits remain. Gradually pour in the cold water and pulse just until the dough starts to form. Transfer the dough to the prepared pan and press it across the bottom and up the sides (about 1½ to 2 inches high). Chill in the fridge for ~20 minutes. Then bake for about 15‑20 minutes; it will still look pale and not fully cooked. Remove and let cool while you make the filling.

Make the caramel for the filling: In a medium saucepan combine the sugar, water, and cream of tartar. Over medium heat melt and cook until the mixture bubbles and then turns a rich deep brown—about 8‑10 minutes. Once the color is right, remove from heat, and slowly whisk in the heavy cream (careful—it will bubble). Whisk until smooth and set aside.

Make the pumpkin filling: In a separate bowl whisk together the pumpkin puree, brown sugar, flour, eggs, and all the spices (cinnamon, nutmeg, ginger, cloves). Then pour in the caramel and whisk until the mixture is smooth and uniform.

Assemble and bake: Place the cooled crust (ideally on a baking sheet to catch any drips) and pour in the pumpkin filling—fill very close to the edge. Bake for about 35 minutes, or until the tart is just set and no longer wobbly in the center.

Make the candied walnuts: To prepare the candied walnuts, begin by lining a baking sheet with parchment paper. In a saucepan combine the sugar and water, melt until golden, then add the walnuts. Stir carefully until the sugar caramelises around the walnuts (watch closely so they don’t burn). Transfer to the parchment and allow to cool and harden. Once firm, roughly chop.

Finish: Once the tart has cooled sufficiently, sprinkle or arrange the chopped candied walnuts on top of the pumpkin‑caramel surface. Serve slightly warm or at room temperature, optionally with whipped cream.