In a saucepan on medium-high heat, add the butter, chicken stock and thyme. Simmer until the thyme wilts slightly, about 8 minutes. Add the corn and stir to break up any chunks. Simmer for about 10 minutes. Remove from the heat, remove the sprigs of thyme, add the sour cream and season with salt and pepper. Stir to blend, and then serve with a dash of cayenne pepper.