Prepare the Roux: In a large, heavy-bottomed pot or Dutch oven, melt the two sticks of butter or margarine over medium heat. Once melted, add the 2 teaspoons of salt and 1 teaspoon of pepper. Stir well.

Create the Thickener: Gradually whisk in the 1 1/3 cups of flour. Continue whisking constantly for 1-2 minutes, allowing the flour to cook slightly and form a smooth paste (this is called a roux). This step is important to prevent a raw flour taste.

Whisk in Liquids: Slowly pour in the 6 ½ cups of milk and 4 cups of chicken broth all at once, while continuously whisking to prevent lumps. Continue to whisk as the mixture heats up.

Thicken the Sauce: Bring the mixture to a gentle simmer over medium heat, stirring frequently. The sauce will gradually thicken as it cooks. Continue to cook and stir for about 5-7 minutes until the sauce is smooth, creamy, and coats the back of a spoon. If the sauce becomes too thick, you can add a little more milk or broth until it reaches your desired consistency.

Add Turkey and Vegetables: Reduce the heat to low. Stir in the 8 cups of chopped cooked turkey and the 16 oz bag of frozen peas. If using, add the drained 8 oz can of sliced mushrooms.

Simmer and Serve: Gently heat the mixture for another 5-10 minutes, or until the turkey and peas are thoroughly heated through and the flavors have melded. Do not boil, as this can cause the sauce to separate.

Prepare Toast: While the A-La-King is simmering, toast two slices of bread per serving.

Assemble and Enjoy: Spoon a generous amount of the hot Turkey A-La-King over each piece of freshly toasted bread. Serve immediately.