Set out a heavy skillet. Put the grated Cheddar Cheese in a bowl and add the sour cream and egg yolks, mixing well after each addition. Add the flour salt thyme and dry mustard, which have been mixed well in a separate bowl or cup. Melt the butter in the skillet over low heat and drop the batter by tsp into the skillet. Cook over medium heat until lightly browned on the bottom. Loosen the edges with a spatula, turn and lightly brown the other side. Serve at once with bacon or pork sausage. Makes about 2 dozen 8 cm cakes.