We made a double recipe which worked fine, and did two large loaves of round spiral bread instead of braided loaves, since it was for Rosh Hoshanah and round loaves are traditional. Highly recommended!
Pumpkin Challah (makes 1 large loaf)
2 1/4 tsp active dry yeast
1/2 tsp ground cardamom
1/2 tsp ground ginger
3 1/2 cups flour
2/3 cup warm water
3/4 cup pumpkin puree
1/4 cup raw sugar
1 1/2 tsp salt
1/4 cup vegetable oil
1/4 cup soy yoghurt
Mix the yeast in the warm water along with the spices and 2/3 cup of the flour. Let the mixture stand for 10-20 minutes. Whisk the sugar, salt, oil, yoghurt, and pumpkin in a large mixing bowl. Add the yeast sponge. Stir in about 2 cups of the remaining flour, then start incorporating the rest with your hands. You might need a bit more or a bit less. The dough should be soft but not too sticky. Knead for 10 minutes. Dough should be smooth. Place the dough in a clean, oiled bowl, cover, and let it rise in a warm place until it has tripled (2-3 hours).
Punch the dough down. On a lightly floured surface, cut it into 6 equal balls of dough. Roll each one into a rope about 3/4'' in diameter. Try to make the ends of the ropes taper. Braid into a 6-strand braid-- see link above. Place on a parchment-lined baking sheet, and rise until at least doubled in size, about an hour.
Preheat the oven to 350 F. Brush the loaves with soymilk, and bake then for 40-45 minutes, until they are deep golden brown and hollow when tapped on the bottom. Take them out of the oven and brush them again halfway during baking.
(Adapted from Maggie Glazer's A Blessing of Bread: The Many Rich Traditions of Jewish Bread Baking from Around the World.)