In a large skillet, melt 1 tablespoon of the butter over medium-high heat. Add the shallots and cook, stirring, for 30 seconds. Add the mushrooms, salt, and black pepper and cook, stirring, until the mushrooms give up their liquid and begin to color, 4 minutes. Stir in the parsley, remove from the heat and set aside.
Preheat the broiler and move the baking rack to the highest position. Line a heavy baking sheet with aluminum foil and set aside.
In a medium saucepan, melt the remaining 2 tablespoons butter over medium-high heat. Add the flour and cook, stirring, until thick, about 3 minutes, being careful not to let the flour brown. Using a whisk, add the milk in a steady stream and cook, whisking constantly, until thick and smooth, 3 to 4 minutes. Add the salt, pepper, Essence, and cayenne and stir well. Add 1/2 cup of the cheese, stir, and cook over low heat until very thick and the cheese is melted, 2 to 2 minutes. Remove from the heat.
Place the toasted bread on the prepared baking sheet and divide the turkey among the toasts. Arrange the mushrooms on the turkey, spread the sauce over the top out to the edges of the turkey, and sprinkle each with 2 tablespoons of the remaining cheese. Place under the broiler until bubbly and the cheese starts to brown, 1 1/2 to 2 minutes, being careful not to let the cheese burn. Remove from the oven.
Transfer the Hot Browns to 4 plates. Arrange 2 slices of bacon over each, garnish with additional parsley and the chives, and serve immediately.