1 egg yolk
1 tablespoon all-purpose flour
2 tablespoons butter
2 teaspoons Dijon mustard
A few dashes hot sauce
1 cup milk
2 teaspoons Worcestershire sauce
1/2 pound shredded extra-sharp yellow cheddar cheese
Place the yolk in a mixing bowl and reserve. Place a heat-safe fondue pot or a medium saucepot over medium heat with the flour and butter, cook for a minute, then whisk in the Dijon, hot sauce and milk.
Right before the milk comes up to a simmer, turn the heat down to medium-low and add in the cheese, slowly stirring in figure-eight motion to melt.
Once all the cheese has melted, remove a ladleful of the hot cheese mixture and whisk it into the egg yolks to temper the yolks, then whisk the egg yolk mixture back into the hot cheese mixture.