Heat the over to 400°F. Cut the pumpkins in half. Scoop out the seeds and place on a baking sheet; bake for 1 to 1.5 hours.
When the pumpkin is cooked + cool enough to handle, scoop out the flesh. This should make about 5 cups. Add butter to a large pot or dutch oven, on medium heat; add shallots and garlic. Sauté until tender.
Add pumpkin and broth to the pot, along with sage, salt and pepper and bring to a boil. Simmer, cover for about 15 minutes.
Blend in a blender until smooth. Garnish with a Greek yogurt and sage.