For the chard:
Wash the chard leaves and run them through a salad spinner.  Cut the stems off the chard, chop and set aside.  Then roughly chop the chard and set the leaves in a bowl.

Melt 1 tablespoon butter in a stir fry skillet.  Add the onion and saute until lightly brown. Add the chard stems, a pinch of nutmeg and a little salt and pepper.  Cook until tender, then add the Swiss chard leaves. Cook everything for another 2 minutes or until the chard leaves are wilted.  Place Swiss chard mixture in a strainer to drain.  Make sure you get all the excess liquid out by pressing a spatula against the chard and strainer. Set aside.

For the sauce:
In a sauce pot  over medium heat, melt 1 tablespoons of butter. Add the garlic and saute for a minute. Whisk in the flour and then the milk. Stir until thickened {about 2 minutes}. Remove from heat and set aside.

To assemble the gratin:
Using your best OCD skills, arrange half of the sweet potato slices in the bottom of a buttered 9 casserole dish. Add salt and pepper, 1/2 teaspoon Italian seasoning.  Next add 1/2 of the drained chard mixture followed by 1/3 cup of cheese.  Pour 1/2 cup of the sauce mixture over the top.  Add a second layer. And more sauce, then sprinkle the remaining cheese over the top.

Bake at 400 degrees for 45 minutes uncovered.  If the cheese starts to brown to much before the cooking time is over, cover it loosely with foil. Cool  about 10 minutes before serving.