Start by melting butter in a saucepan and then add the flour. Stir over a medium heat to form a roux base.
Then slacken by adding milk and all of the cheese. Stir on a low heat for 5-6 mins to make a smooth, glossy cheese sauce.
Remove from the heat and continuing to stir add mustard and a beaten egg yolk. Season to taste and allow to cool.
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Lightly toast your bread and slice into toast fingers. Preheat your grill and then spread the cheese sauce over the toast.
Grill for 2-3 mins on high heat until the cheese caramelises. Then transfer to a platter and drizzle with lots of Truffle Honey, A good pinch of Truffle Sea Salt and serve with ketchup and other delicious Truffle condiments of your choice.