In a food processor, process the walnuts into small crumbs. Add the pitted dates and process until finely chopped. The mix will be sticky.
Add the sea salt, coconut oil, cinnamon and nutmeg, and process until thoroughly combined into a crumbly but sticky dough you can press together with your fingers.
Prepare 6 muffin tins with paper liners or use 6 mini-tart pans. Divide the dough between the 6 servings then use your fingers to firmly press the dough down into the cups for a tight fit. Place in the fridge to chill while you make the top layer filling.
In a small mixing bowl, combine melted coconut butter, pumpkin puree, maple syrup, allspice, nutmeg, clove, and cinnamon. Stir until everything is incorporated and smooth.
Remove the chilled tarts from the fridge. Spoon the pumpkin filling over the bottom base layer and smooth to even out. Garnish the tops with a single walnut. Place in the freezer until set, about 30 minutes.
Once the tarts are firm to the touch, pop out of the tray and serve topped with whipped cream.