In medium bowl, stir water and yeast until combined. Let sit 10 minutes until slightly foamy.
Meanwhile, in large bowl or bowl of stand mixer, stir flours, pumpkin pie spice and salt until combined.
Once yeast mixture is foamy, whisk in pumpkin puree, honey, vegetable oil, egg and egg yolk until just combined.
Make well in flour mixture. Pour pumpkin mixture into well. Use wooden spoon or dough hook of stand mixer on low speed to stir until dough forms. Knead dough by hand 10 minutes, adding more flour as needed just until soft, smooth, elastic dough forms; OR, use dough hook of stand mixer on medium speed to knead dough 5 minutes, adding more flour as needed just until soft, smooth, elastic dough forms.
Shape dough into ball. Return to bowl. Cover with plastic wrap and let rise in warm place 1 1/2 hours until doubled.
Heat oven to 350 degrees F. Line baking sheet with parchment paper. Punch down risen dough. Divide into 3 equal pieces. Roll each piece into 14-inch long log. Braid dough, tucking ends under dough. Cover loaf with towel and let rise 45 minutes until doubled.
Make the egg wash by beating together egg yolk and water. Brush top of loaf with egg wash, then sprinkle with sesame seeds, if using. Bake 35 to 40 minutes until golden brown and baked through.