In a large, deep skillet, heat the oil over high heat. Add the onions and cook until golden brown and tender, 5 minutes. Add the mushrooms, 1/2 teaspoon of the garlic, 1 1/2 teaspoons of the Essence, 1 teaspoon of the salt, and 3/4 teaspoon of the pepper, and cook, stirring, until the mushrooms are tender and have given off their liquid and are tender, about 5 minutes. Add the beer and cook, stirring, to deglaze the pan and until the mixture is almost dry, 1 to 2 minutes. Remove from the heat and let cool.
In a large bowl, combine the eggs, cream, molasses, Worcestershire sauce, thyme, remaining 1 1/2 teaspoons of Essence, remaining 1/2 teaspoon of salt, and remaining 1/4 teaspoon of pepper, and whisk well to blend. Add the cheeses and stir well. Add the bread cubes and let sit until the bread has absorbed the liquid, about 2 hours.
Preheat the oven to 350 degrees F.
Butter a 9 by 13-inch baking dish with the butter. Add the bread crumbs, shaking to cover the bottom evenly. Pour the bread pudding mixture into the prepared pan and cover with aluminum foil. Bake for 1 hour and uncover. Continue baking until the pudding rises and is firm in the center, and golden brown, 20 to 30 minutes.
Let cool slightly before serving.
Yield: 6 servings