Grate the cheeses into a bowl and add the cornstarch. Toss to evenly coat.
In a saucepan, over low heat, simmer the wine and lemon juice.
Slowly add the cheeses (one small handful at a time) and stir constantly.
As you very slowly melt and stir the cheeses, continue to stir so that the cheese mixture will be smooth. Be patient on this step so that your cheese does not become a ball.
When cheese mixture is melted and smooth, stir in the mustard and the splash of Worcestershire Sauce.
Transfer fondue to a fondue pot and keep warm.