Mix the dough. There are two ways to do this depending on which yeast you use. Follow only the method that matches your yeast, then continue with the rest of the recipe.
METHOD A: INSTANT YEAST (no pre proofing needed)
In a large bowl, whisk together the bread flour, salt, and instant yeast. In a separate bowl, whisk the warm water, room temperature pumpkin puree, brown sugar, and vanilla until smooth, then pour it into the flour and mix until no dry flour remains. The dough will be sticky and shaggy.
METHOD B: ACTIVE DRY YEAST (proof the yeast first)
In a large bowl, combine the warm water, active dry yeast, and a pinch of the brown sugar. Let it sit for 5 to 10 minutes until foamy and bubbly. If it does not foam, your yeast is dead, so start over with fresh yeast. Whisk in the room temperature pumpkin puree, the remaining brown sugar, and the vanilla until smooth, then add the flour and salt and mix until no dry flour remains. The dough will be sticky and shaggy.
Rest. Cover the bowl and let the dough rest for 30 minutes at room temperature.
Stretch and fold, set 1. With wet hands, grab one side of the dough, stretch it up, and fold it over itself. Rotate the bowl and repeat, going all the way around the dough 4 to 6 times. Cover and rest 30 minutes.
Stretch and fold, set 2. Repeat the same stretch and fold around the bowl. Cover and rest 30 minutes.
Stretch and fold, set 3. Repeat the stretch and fold one more time. The dough will feel noticeably smoother and stronger.
Bulk fermentation. Cover and let the dough rise at room temperature until fully doubled, puffy, and domed with bubbles, about 1 to 2 more hours. The pumpkin makes this a heavier dough, so go by the rise rather than the clock.