Although it is not mandatory, I recommend using homemade pumpkin puree in this recipe, because it gives richer flavor.
BAKED PUMPKIN PUREE:
Cut 1 medium or small pumpkin in half, stem to base. Remove seeds and pulp. Grease the pumpkin with a little vegetable oil and bake at 350F until it gets soft and chars slightly. It takes about 1 hour (+-20 minutes) depending on how thick the pumpkin is.
Once cooked through, scrape the pumpkin meat from the shell halves and puree in a blender until smooth.