While pumpkins are cooking bring chicken stock to a simmer and leave on low heat.
In a sauté pan melt first 2 tablespoon butter.
Add onion and sauté until softened, about 5 minutes.
Add grated pumpkin and cook, stirring, for 1 minute.
Add rice and stir well until rice grains are coated with butter.
Add first ½ cup hot stock and set a stopwatch* to start timing. Stir the mixture until the liquid is absorbed.
Adjust the heat to a low simmer so each addition of liquid is absorbed in 2-3 minutes.
Continue adding stock ½ cup at a time, stirring frequently.
Taste for doneness at 18 minutes. Continue adding stock until the rice is done and has a nice, creamy texture. Al dente the Italians would say.
Remove from heat and stir in remaining 2 tablespoon butter and Parmesan cheese.
Taste and adjust seasoning with salt and pepper.
Spoon risotto into cooked pumpkins and add pumpkin lid. Reheat in oven if needed. Serve warm.