Preheat the oven to 350 degrees.
Blanch the Haricot Vert: process batches through boiling, lightly salted water for 1 ½ minutes then place them into an ice bath (large mixing bowl of cold water and ice) until they are full cooled. Place them on a clean kitchen towel to drain and pat dry.
In a large pot (or large deep skillet) sauté the bacon over medium-high heat until the fat is rendered (begins to liquefy) and the bacon lightly browns; 2-3 minutes. NOTE: The bacon will not cook fully and should still be pliable. Remove from the pan and set aside.
Add 4 tablespoons of butter to the bacon drippings in the pan and allow it to melt over medium heat.
Add the mushrooms and thyme, a sprinkle of salt and pepper, and sauté until the mushrooms release their moisture and begin to reduce; 3-4 minutes.
Add the shallots and continue to sauté until the shallots begin to turn translucent.
Add the bacon and haricot vert to the mixture and stir to fully incorporate. Remove from heat.
In a large saucepan melt remaining 4 tablespoons of butter over medium heat.
Once the butter is melted whisk in the flour forming a roux (a thickener base for French sauces). Slowly pour in the milk and chicken stock, whisking constantly to fully mix together smoothly. Continue to stir the roux over medium heat until it thickens (3-5 minutes).
Add the cheese to the roux, whisking to help melt the cheese and to make a smooth mixture.
Add the cheese sauce, along with ¾ teaspoon of each Kosher Salt and Pepper, to the bean mixture. Stir well to mix all the ingredients together.
Spoon mixture into a 13 x 9 inch 4-quart baking pan and smooth to uniformly fill the pan.
Mix together the bread crumbs and chopped almonds and spread evenly over the top of the casserole.
Bake for 30 minutes or until heated through.