Preheat oven to 350 F. Grease a 1 ½ quart casserole dish; set aside.

In a medium saucepan over medium-low heat, melt butter.

Stir in flour, and cook for 1 minute.

Add milk, and whisk to combine.

Stir in mustard, salt, pepper, and thyme.

Cook until milk thickens (it will be the consistency of a cream soup), stirring occasionally.

Reduce heat to low, and stir in cheese.

Place half of the sliced potatoes in prepared casserole dish.

Pour 2/3 cup of cheese sauce over potatoes.

Repeat layer with remaining potatoes.

Dot cream cheese over potatoes.

Cover cream cheese and potatoes with remaining cheese sauce.

Cover and bake for about 60 minutes.