- Butter a 9x13-inch baking dish, and preheat the oven to 400°F.
- Over medium heat, melt the 1-1/2 tablelspoons butter and stir in the fresh bread crumbs.
- Sauté until golden, remove from heat and set aside.
- In a small bowl, combine the flour, thyme, salt and pepper.
- Put one-third of the sliced potatoes into the buttered baking dish.
- Sprinkle one-third of the flour mixture evenly over the potatoes, and top with half of the onion rings.
- Repeat for the second layer, then top with the remaining one-third of the potatoes and flour mixture.
- Whisk together the chicken broth, cream and mustard, and pour mixture evenly over the potatoes.
- Bake for 30 minutes, then scatter the bread crumbs over the potatoes.
- Continue baking for 50 to 60 minutes longer.
- Potatoes should be crusty and medium brown on top, but tender and creamy in the middle.
- Most of the liquid will be absorbed, but potatoes should still be moist.
- Serve warm.
Ready in: 2 Hrs 5 Min