Potatoes au Gratin
3 Tbsp butter
1/2 onion, small dice
1 Tbsp chopped sage
1 tsp chopped rosemary
3 Tbsp all-purpose flour
3 cups milk
8 oz. gruyere cheese, grated (about 2 cups)
6 medium russet potatoes
Salt and pepper to taste
3 Tbsp butter
1 cup panko or other bread crumbs
Preheat oven to 400 F
Melt butter in a medium pot and add diced onion. Add sage and rosemary and cook over medium heat for 5 minutes.
Gradually add flour while whisking to make a roux and cook for another few minutes, whisking occasionally until roux is a light blonde.
Gradually add milk while whisking to work out any lumps and bring to a simmer. Cook for a few more minutes, whisking regularly.
Add 1 cup (about half) Gruyere cheese and whisk until melted and smooth. Taste the sauce and add salt and pepper if desired. Allow to cool slightly.
Peel your potatoes and immediately submerge completely in cold water. Using a mandoline, slice 1/8″ thick.
Spread a thin layer of sauce in the bottom of an oven safe dish.
Working around the edge of the dish, shingle the potato slices until the dish is filled and spread another layer of sauce on top.
Continue layering until you use your all of your sauce on top of the last layer.
Sprinkle some of the remaining cheese on top so it is partially covered.
Melt butter and toss with bread crumbs and remaining cheese. Spread evenly over the top of the casserole.
Bake at 400 F for one hour. Check at 30 minutes. The topping should be nicely browned. Cover with aluminum foil and cook 30 more minutes.
Remove from oven and allow to cool 10 minutes before serving.