Melt the butter in a heavy-bottomed saucepan over medium heat. Cook the eschallots until soft and translucent, about 3 minutes. Add the water and peas. Bring to a boil, then reduce heat to low, cover, and simmer until the peas are tender, 12 to 18 minutes.
Puree the soup in batches in a blender or food processor. Strain back into the saucepan, stir in the cream if using, and reheat. Season to taste with salt and pepper before serving.