In a medium Dutch oven or pot over medium heat, melt 2 tablespoons butter.
Add onions and saute until translucent, about 3-4 minutes.
Add lemon juice and Riesling and bring to a light simmer to cook off the alcohol, about 3 minutes.
Add pumpkin, chicken stock, salt, and pepper.
Using an immersion blender, blend the pumpkin with the onions (or blend in a blender). Bring the soup back up to a simmer and simmer for 10 minutes for the flavors to blend. Turn off heat and stir in cream.
Garnish with pumpkin seeds (pepitas), chives, red chili flakes, and/or black pepper