Remove stems from the chiles, cut in half lengthwise, and shake out the seeds. Place chiles in a hot dry skillet for a minute or two until they smell fragrant.
Put the chiles in a bowl and add enough boiling water to barely cover. Soak the chiles for about 30 minutes, until they feel soft and leathery.
Drain and discard the soaking liquid. Place chiles in a food process and process until smooth and paste like. Combine with the cream in a small saucepan.
Bring the cream to a slow simmer over medium heat, while whisking. Take the pan off the stove and let it sit for 5 minutes to give the flavor of the chiles time to infuse.
Put the pan back on medium heat and simmer, while whisking, for 30 seconds to 2 minutes, until the sauce has the consistency you like. Season to taste with salt.