Step 1Process the cashews in a food processor until very fine.
Step 2Cream the butter and sugar in a stand mixer or in a large bowl using a hand mixer. Add the cashews to the butter-sugar mixture; mix until combined. Scrape down the sides of the bowl.
Step 3Add the orange zest, egg and vanilla extract, scraping down the sides again. Add the flour and salt and mix until well combined.
Step 4Roll the dough between two sheets of parchment paper into a large rectangle, slightly larger than 12 inches by 16 inches and about 1/8 -inch thick. Place the rolled dough flat on a pan and freeze it for 2 to 3 hours until stiff.
Step 5Heat the oven to 350 degrees. Using a ruler, cut the dough into pieces to fit the bottom of the pan and all of the sides of the pan. Once your dough is cut into the exact dimensions, peel away one the parchment paper and fit the pieces of dough in the sheet tray. Seal any cracks by pressing the dough together with your fingertips. Bake until very golden brown, about 25 minutes. Set aside and allow to cool while you make your tart filling.
Step 1Heat the oven to 350 degrees. Whisk one of the eggs into the pumpkin puree (by hand or in a stand mixer). Crack the other egg into a small bowl and whisk to combine the yolk and white; add half of the combined egg to the pumpkin mixture. Discard the other half or reserve it for another use. Add the sugar, brown sugar, salt, cinnamon, ginger and nutmeg to the puree and mix until incorporated.
Step 2Slowly add the milk and condensed milk. Pour the filling into the baked tart shell. Bake on the center rack for 30 to 45 minutes (turning once during baking), until the filling is set and a toothpick inserted in the center comes out clean. Allow the tart to cool.
Step 3When cooled, place the tart in the refrigerator. To serve, slice the tart lengthwise in half, then slice each half into eight slices. The tart will keep for 2 days, refrigerated.