Melt the butter in a large skillet over medium heat. Cook celery and shallots until shallots are tender. Pour half n half into a large pot over medium high heat. Mix in melted butter, celery and shallots. Stir continuously. When the mixture is almost boiling, pour the oysters and their liquid into the pot. Season with salt, pepper and cayenne pepper. Stir until the oysters curl at the ends. When they curl, the stew is finished cooking.