In a medium bowl, stir the yeast, 1 teaspoon of sugar, and the warm water together. Set aside until yeast begins foaming, about 5-10 minutes.

In a large bowl, whisk the ⅓ cup sugar, flour, cinnamon, cardamom, and salt together.

Add the pumpkin, vegetable oil, and 2 eggs to the activated yeast. Whisk to combine.

Make a well in the center of the flour mixture, then pour in the liquid ingredients. Stir gently to form a loose, wet dough. Turn the dough out onto a lightly floured surface and knead, adding a little more flour as necessary to keep the dough from sticking, until a smooth and supple dough ball forms, about 8-12 minutes.

Lightly oil a large bowl, place the dough ball in the bowl, and turn to coat the dough. Cover with a clean dish towel or plastic wrap and place in a warm spot until almost doubled in size, 1 - 1 ½ hours.

Line two 9-inch round cake pans with parchment paper circles. Lightly grease the parchment.

Gently deflate the dough by lightly pressing the center. Turn the dough out onto a clean, lightly floured flat surface, then divide in half. Cover one piece with a dish towel.

Working with the other piece, roll it out into a large rectangle to ⅛-inch thick (about 10-by-18-inches). Cover the surface of the rectangle with an even layer of ½ the apple butter (⅔ cup), going out to ½-inch from every edge.

Starting along a long edge, tightly roll the dough into a spiral. Seal the ends by pinching them, then gently, carefully stretch the rolled-up dough out to 24-inches long. Starting at one end, coil the rope of dough into a spiral, tuck the end underneath, and place into a prepared pan. Repeat with the second piece of dough.

Whisk the egg yolk in a small bowl. Brush the challah spirals with the egg yolk wash. Cover both spirals with lightly oiled plastic wrap and set aside to rise for 30 minutes. Meanwhile, preheat the oven to 375˚F. Put the leftover egg yolk wash in the refrigerator.

After the 30 minute rise, apply a second coat of egg wash. Bake for 40-55 minutes, until the loaves are a deep golden brown and an instant-read thermometer reads 195˚F from the center of the loaf.

Cool completely or serve warm. Challah is best fresh, but it can be stored for up to 3 days or sliced and frozen.