To toast the curry place it in a small skillet over medium heat. Heat the curry stirring occasionally with a wooden spoon until fragrant, about 5 to 8 minutes.
Melt the butter in a large stockpot over medium heat. Add the sliced onion and scallions and sauté until very soft, about 10 minutes.
Pour in the chicken stock and add the pumpkin puree, the bay leaves, sugar, curry powder, nutmeg, parsley, kosher salt, and pepper.
Stir to blend together and bring the soup to a simmer over medium heat. Reduce the heat to medium-low and continue simmering, uncovered for 30 minutes.
Remove the bay leaves from the soup and slide the pan off the heat.
Using an immersion blender or purée the soup until smooth. You can also transfer the soup to a blender and process.
Return the soup to a low heat and add the half and half. Simmer over medium heat an additional 10 minutes to warm through.
Top with a sprinkling of grated Parmesan if desired.