1. In a large bowl, place the yeast, warm water, and one teaspoon of sugar and stir. Let the mixture sit for 10 minutes, or until thick.
2. Add the remaining sugar, brown sugar, soy milk, margarine, egg, pumpkin purée, salt, cinnamon, nutmeg, vanilla, and 2 cups (250 grams) of the flour to the bowl and mix on low speed with either a dough hook in a stand mixer or a wooden spoon. Add another cup (125 grams) of flour and mix well. Add more flour, a tablespoon at a time, and mix it in until the dough becomes smooth, scraping down the sides of the bowl each time before adding more flour.
3. Cover the dough with a clean dishtowel and let it rise for one hour in a warm place. I use a warming drawer on a low setting, or you can turn your oven on to its lowest setting, wait until it reaches that temperature, place the bowl in the oven, and then turn off the oven.
4. Punch down the dough by folding it over a few times and reshaping it into a ball. Then re-cover the dough and let it rise for 10 minutes.