Preheat oven to 400F and line a baking sheet with parchment paper.
Slice pumpkin in half and remove seeds. Stab fork into each side of the pumpkin's skin 3-4 times. These holes allow steam to escape when roasting in the oven.
Slather sweet potatoes and pumpkin halves in vegetable oil. Place pumpkin flesh sided own on the parchment paper.
Roast pumpkin and sweet potato for 45-50 minutes. You'll known when they are finished baking when you insert a pairing knife into the vegetable flesh and it easily slides in and out.
Let roast pumpkin and sweet potatoes cool. Once at room temperature scoop the pumpkin away from the skin into a measuring cup. Slice roasted sweet potatoes in half and similarly scoop out the flesh to be measured.
Melt butter over medium heat in a large dutch oven. Add the onions and cook, stirring occasionally, until soft, approximately 5 minutes.
Add roasted sweet potato and pumpkin to the onions and stir in chicken broth, salt and pepper. Simmer for 3-5 minutes while stirring.
Add sliced apple, honey, ginger, maple syrup and spices.
Using an immersion blender, puree the soup until thick and creamy.
Slowly stir in room temperature milk then simmer while stirring for 2-3 minutes until desired consistency is reached.
Use a ladle to pour Roasted Pumpkin and Sweet Potato Soup into bowls. Top with a dollop of sour cream and chopped parsley.