Cut the top of the pumpkin to open it. Use a spoon to remove the inside from the pumpkin, which you will cut into pieces. Be careful not to cut too much of the bottom of the pumpkin, because otherwise it might break later on. Thus, keep the bottom rather thick.
Sweat the pumpkin's inside with the leek, onion, 3.5 oz. butter, 0.5 gallons water (or better: bouillon), salt and pepper.
After thirty minutes cooking, take the electric mixer and stir well. Add the cream and butter, as if you would prepare a normal potage. Continue until obtaining a smooth cream.
In the meanwhile, open the clams a la vapor. Then, recover the meat from each shell. Season.
Add the clams at the very end to the pumpkin cream.
Be aware that from now on, once the clams are in the pumpkin cream, the mixture should not boil anymore.
Now, carefully pour the pumpkin cream into the prepared pumpkin. Place the lid back on the pumpkin to close it and keep it warm. Serve and enjoy!