Shrimp in Pumpkin Seed Sauce

Place the shrimp in a large saucepan with the water, salt, pepper, cumin, oregano, and onion.
Bring to a boil, over medium heat.
Reduce heat to low and simmer until the shrimp are pink and curled, about 3 minutes.
With a slotted spoon, lift the shrimp and onion from the cooking liquid.
Save the cooking liquid to use for the sauce base.
Set the onion aside on a plate.
When the shrimp are cool enough to handle, peel and devein.
Put the shrimp shells in the pan of cooking liquid.
Put the cleaned shrimp in a bowl and set aside.
Bring the liquid with shrimp shells to a boil, reduce the heat to low, cover and simmer 10 minutes.
Pour the shrimp broth through a strainer into a bowl.
Reserve the broth and discard the shells.
In a dry skillet, toast the pumpkin seeds, stirring constantly, until they pop about in the pan and are aromatic.
Spread the seeds out on a plate to cool; then grind to a powder in a spice grinder.
(I use a coffee grinder reserved for spices.
)
Put 2 cups of the shrimp broth into a blender jar.
Add the ground pumpkin seeds, reserved onion, cilantro, and serranos.
Blend until smooth.
In a large saucepan, melt the butter over medium heat.
Pour in the blended sauce and cream.
Bring to a boil; then reduce heat to low, and cook, stirring frequently, about 8 minutes.
Stir in the shrimp.
Heat through.
Adjust seasoning, if needed.