Preheat the oven to 425°F (220°C). Line a large rimmed baking sheet with parchment paper if desired.
Place the pumpkin cubes, sliced apples, chopped onion, and whole garlic cloves on the baking sheet.
Drizzle everything with olive oil. Sprinkle with cinnamon, nutmeg, ginger, salt, and black pepper, then toss until evenly coated.
Arrange the ingredients in a single layer, leaving a little space between the pieces to encourage caramelization.
Roast for 30–35 minutes, stirring halfway through, until the pumpkin is fork-tender, the onion has softened, and the apples have caramelized around the edges.
Remove the baking sheet from the oven and let the roasted ingredients cool slightly.
Carefully transfer the roasted pumpkin mixture to a blender. Add the vegetable broth and blend until completely smooth. Work in batches if necessary and use appropriate precautions when blending hot ingredients.
Pour the blended Creamy Roasted Apple Pumpkin Soup into a large saucepan or Dutch oven.
Stir in the heavy cream and warm gently over medium-low to medium heat for 5–7 minutes. Stir occasionally and avoid bringing the cream to a vigorous boil.
If the soup is thicker than you prefer, gradually stir in additional vegetable broth until it reaches your desired consistency.
Taste and adjust the salt, black pepper, cinnamon, or other spices as needed.
Ladle into bowls and garnish with toasted pumpkin seeds and a small swirl of cream, if desired. Serve warm.