In a medium saucepan, melt 2 tablespoons of the butter over medium heat. Add the flour and cook for 1 minute, stirring constantly. Slowly whisk in the beer. When the bubbles have begun to subside, add the cheeses, 1 handful at a time, stirring constantly and in 1 direction only, until smooth and creamy. Add 1 teaspoon of the Essence, the Worcestershire sauce, and the dry mustard and stir to combine. Keep warm while you prepare the oysters.
In a small skillet or saucepan, melt the remaining tablespoon of butter over medium-low heat and add the oysters. Cook for 1 1/2 to 2 minutes, or until the oysters are just cooked and have begun to curl around the edges, stirring occasionally. Season with the remaining 1/2 teaspoon of Essence.
To serve, divide the French bread toast between 6 plates, and divide the cooked oysters among the toasts. Top with the cheese mixture, and garnish with the crispy bacon.
Combine all ingredients thoroughly and store in an airtight jar or container.
Recipe from "New New Orleans Cooking", by Emeril Lagasse and Jessie Tirsch. Published by William and Morrow, 1993.
If you cannot find Caerphilly cheese, substitute cheddar.