Cook spinach as directed on the package; drain and squeeze out water
Cut the mushrooms into quarters, finely chop the shallots and garlic
Grate the cheese, measure remaining ingredients
Prepare a baking dish with butter, preheat the oven to 350 degrees Fahrenheit
Combine the spinach and vegetables
Add 2 tablespoons of butter to Dutch oven over medium heat
Add the mushrooms and sauté them for about 10 minutes, until liquid is released and reduced
Add the shallots and sauté until starting to clear-about 3 to 4 minutes.
Add the garlic and the Herb and Spice Blend. Mix well and sauté until aromatic-about 1 to 2 minutes
Continue sautéing mushrooms and spices for another 2 or 3 minutes, until starting to brown, stirring often so it doesn't stick.
Deglaze the Dutch oven with white wine. Using your spoon, loosen the fond off the bottom of the pan and stir that into the mushrooms. Allow the wine to reduce down almost completely.
Add the spinach to the mushroom mixture and stir to thoroughly blend all ingredients. Set aside.
Prepare the Cheese Sauce
Warm the milk in the microwave or in a saucepan.
Melt the butter in a large saucepan over medium heat.
Add the AP flour and whisk to make a blond roux; about 3 minutes.
Remove the saucepan from the heat and add the warmed milk about ¼ cup at a time, whisking to combine completely with the blond roux before adding more milk.
Once about half of the milk has been added, it's OK to add the remaining milk.
Once the milk has been thoroughly blended with the roux, return the saucepan to the heat and bring to a simmer. Maintain a simmer for about 4 or 5 minutes, whisking constantly. When the sauce coats the back of a spoon it is ready.
Add 1 to 1 ½ cup of grated gouda cheese and 2 tablespoons of Romano cheese to the bechamel sauce and combine thoroughly.
Combine and Bake
Add about 1 ½ cups of the cheese sauce to the spinach and blend well. (You may add more or less than 1 ½ cups of cheese sauce if you desire)
Taste for seasoning and add salt and pepper as needed.
Fold the spinach/cheese mixture into the prepared baking dish.
Top the spinach mixture with the remaining grated gouda cheese and sprinkle romano cheese on top
Place the baking dish, uncovered, into a preheated 350-degree oven for about 30 minutes or until browned on top and bubbly around the sides.
Notes
Keep leftover spinach casserole in an airtight container refrigerated for 3 to 5 days or frozen for about 6 months. Make sure to freeze the spinach dish in an airtight container and thaw in the fridge overnight. Reheat covered in a 350-degree oven for about 10 to 15 minutes or until warmed all the way through. This can also be reheated in the microwave. This recipe is perfect for frozen spinach. Use your favorite brand; mine is the one that comes in a pouch and can be "steamed" in the microwave. Fresh spinach is also fine. You’ll need at least 2 pounds of fresh spinach. You should saute the fresh spinach in a little butter until fully wilted. Whether it's fresh or frozen spinach, make sure to drain and squeeze out any water that is retained. I use Baby Bellas mushrooms which have a rich, earthy flavor. I cut them in quarters so there are chunks of mushrooms throughout the dish, but sliced mushrooms will also be fine. You can substitute white button mushrooms, portobellos or even shiitake mushrooms. Mushrooms have varying amounts of water, so the saute step is important to reduce that water so it does not make the gratin soggy. Saute time will vary depending on the water content of the specific mushrooms you use.I use smoked gouda and grated romano cheese for this recipe. Smoked Gouda is a smooth, rich cheese that melts well and adds some complexity to the flavor profile. The Romano’s sharp, tart taste is a great balance to the creamy smoothness of the gouda. Good substitutes are Gruyere Cheese, Cheddar (smoked cheddar is good!) Monterey Jack and Pepperjack. A combination of some of these cheeses is great in this recipe. Make sure to use a cheese that melts and blends well.