Preheat the oven to 350°F. Lightly grease a 9 x 13 baking dish with butter.

Add dried mushrooms to a small bowl with boiling water. Steep for at least 10 minutes. Once rehydrated, take the mushrooms from the water and roughly chop. Reserve the steeping water.

In a large skillet, warm butter over medium high heat. Once the butter starts foaming, add the diced creminis in an even layer. Do not stir the mushrooms for 3 to 4 minutes. Once golden and caramelized, toss the mushrooms and cook for several minutes on the other side. Add the rehydrated, chopped wild mushrooms to the skillet and cook for 2 to 3 minutes, stirring occasionally.

Sprinkle the mushroom mixture with flour, stirring to coat. Pour in 3/4 cup of the mushroom steeping liquid. You may notice some grit sitting a the bottom of the mushroom steeping liquid. Try to avoid pouring that into your skillet. Add chicken stock then whisk to break up any clumps. Add the milk and cook until the mixture has slightly thickened, stirring frequently.

Take the wild mushroom soup off the heat and stir in the kosher salt, freshly ground black pepper and green beans. Set aside.

Pour about 1/2 inch vegetable oil into a large, heavy bottomed pot. Warm over high heat until the oil is hot, but not smoking. Add the shallots then turn the heat to medium low. Cook the shallots for 15 - 20 minutes until light golden brown, stirring occasionally to keep the shallots from burning and clumping.

Using a slotted spoon, transfer crispy shallots from the oil to a paper towel-lined plate. Stir half of the shallots into the green bean-mushroom mixture. Reserve the other half for topping. Transfer the mixture to the prepared baking dish, cover with foil and bake for 50 - 60 minutes.

Take the casserole from the oven, uncover and spread the remaining fried shallots evenly on top. Bake, uncovered, for 5 - 7 minutes more, or until the topping is crispy and golden. Let stand for 5 minutes before serving.