Step 1

Preheat the oven to 350°F. Grease a 13x9x2-inch casserole dish. Place the chicken in the baking dish, and top with the ham and cheese.

Step 2

In a small saucepan over medium heat, melt the butter. Stir in the flour until a smooth paste forms.

Step 3

Gradually whisk in the milk. Continuing to stir constantly, bring the mixture to a boil. Cook, stirring, until thickened, two to three minutes. Add the lemon juice, mustard, salt and pepper. Editor's Tip: Gradually adding the milk to the roux is the secret to a smooth, lump-free sauce.

Step 4

Remove the saucepan from heat. Pour the sauce evenly over the cheese layer.

Step 5

Place the bread crumbs, butter and parsley in a small bowl, and toss well to coat. Sprinkle evenly over the casserole. Bake, uncovered, for 40 to 45 minutes, until the breadcrumbs are golden brown and the sauce is bubbling. Rest your chicken cordon bleu casserole for five minutes before cutting and serving. Editor's Tip: Allowing the casserole to stand for a few minutes before slicing makes it easier to cut.