Step 1

PREP: Spray a large slow cooker (I use a 6-quart pan) with nonstick spray. Set aside.

Step 2

MUSHROOMS AND ONION: Add the butter to a large and deep skillet set to medium heat. As the butter is melting down, add in the finely diced onion and finely diced mushrooms. Sauté, stirring frequently, until tender, about 5-7 minutes. Reduce the heat if anything is burning.

Step 3

GARLIC AND SEASONINGS: To the skillet, add the minced garlic, garlic powder, onion powder, dried parsley, dried thyme, and salt and pepper to taste. (I add in 1 teaspoon of salt and 1/2 teaspoon pepper, but add to preference -- depending on how salty the chicken broth is, you may want less.) Stir and cook until fragrant, about 1 minute. Sprinkle in the flour and whisk until a thick dough forms. Cook for about 1 minute to eliminate the raw flour taste.

Step 4

MILK AND BROTH: Gradually, while whisking constantly, add in the milk, cooking until thickened. Continue in the same manner with the chicken broth. Reduce the heat and simmer until thickened. Stir in the Dijon mustard.

Step 5

SOUR CREAM AND HASH BROWNS: Remove from heat and stir in the sour cream. Pour this creamy mixture into the base of the prepared slow cooker. Add both bags of hash browns and the freshly grated Cheddar cheese (See Note 1). Stir everything together and press into one even layer (Quickly wipe down the edges of the crockpot to avoid burning).

Step 6

COOK: Place a few sheets of paper towel in between the lid and the crockpot (this helps gather steam and liquid to keep the casserole from getting soggy). Cook on high for 2-3 hours (See Note 2). Remove the lid and if desired, place the casserole base in the oven and broil for 2-3 minutes to get a crispier top and edges. ( Only do this if your cooker crock is oven safe!) Taste the casserole and adjust seasonings -- add more salt and pepper as needed.

Step 7

TOP AND ENJOY: Garnish the casserole with toppings of your choice such as cooked and chopped bacon, thinly sliced chives, etc.