1. Preheat the oven at 350F degrees.

2. Peel the potatoes and slice them thin. A mandoline will give you uniform slices.

3. Heat a medium sized skillet over medium and melt your butter.

4. Sprinkle in your flour, stirring constantly to combine. Allow to cook for several minutes until it begins to smell nutty.

5. Slowly add in your milk, constantly stirring. Continue to stir until the sauce thickens.

6. Add both mustards to the sauce, stirring to combine.

7. Add your seasonings, fresh herbs, and Gruyere cheese.

8. Butter a baking dish and arrange your potato slices. Pour the sauce over the top.

9. Top with more Gruyere cheese.

10. Bake for 45 minutes covered with aluminum foil.

11. Uncover and bake for another 15-20 minutes or until the top is golden brown and bubbly.