Melt butter in a skillet over medium-high heat. Add shallots, and cook 2 minutes or just until tender. Stir in thyme and flour. Add wine, and simmer until slightly thickened.
Place egg yolks in the top portion of a double boiler. Slowly whisk in the butter and shallots. Place the mixture over barely simmering water. Whisk constantly until the egg yolks are thickened, about 2 to 4 minutes. (Do not let the yolks get too hot, or the mixture will scramble.) Stir in salt.
Place sauce in a bowl of warm water until serving. If mixture thickens, thin with a small amount of water.
