Ingredients:
6 medium Yukon Gold Potatoes
Cheese Sauce:
4 Tablespoons butter
1 yellow onion, sliced into strings
3 cloves garlic,, minced
¼ cup all-purpose flour
1 1/2 cups half and half, or milk
3/4 tsp dried rosemary
1/2 tsp dried oregano
1/2 tsp dried thyme
1/2 tsp sage
2 cups cheddar cheese,, shredded
1/2 cup Gruyere cheese,, shredded
1 cup cooked ham, diced
Topping/Garnish:
1/4 cup Parmesan, finely grated into a powder
1 Tablespoon Fresh Parley, roughly chopped
Instructions:
Preparing the Cheese Sauce:
-Shred the cheddar and Gruyere cheese and set aside, it should be close to room temperature when mixed into the sauce. **Reserve 1/2 cup of the cheddar to top the casserole with.
-Melt the butter in a medium saucepan over medium heat. Add the sliced onions and cook onions for 20 minutes (or more), stirring occasionally. They should begin to brown and caramelize.
-Add the minced garlic and cook for 1 minute. Gradually add the flour, and mix constantly to form a paste. Heat for 1 minute.
-Temper the half and half/milk by heating it in the microwave for 30 seconds. Add it to the saucepan and stir to combine.
-Add the 3/4 tsp of rosemary, then 1/2 tsp each of oregano, thyme, and sage. Simmer for 5 minutes. Remove from heat.
-Gradually sprinkle in 1 + 1/2 cups of the shredded cheddar and 1/2 cup of the Gruyere until smooth and well combined.
-Mix in the ham, you may want to reserve some to top the casserole with.
Assemble the Casserole:
-Preheat the oven to 400 degrees.
-Peel the potatoes and slice them thinly, about 1/8 inch thick. (A mandoline slicer makes this much easier.)
-Lay 1/3 of the potatoes in a single layer, overlapping each other, on the bottom of a lightly greased 9 x 13 casserole dish. Season lightly with salt and pepper if desired.
-Spoon 1/3 of the cheese sauce over the potatoes and use a pastry brush to completely cover the potatoes with the sauce, to retain their color.
-Repeat twice more until all of the potatoes and sauce are layered in the casserole dish. Top with remaining cheddar cheese and any reserved diced ham.
-Bake, covered, for 30 minutes. If making ahead: Let it cool completely and freeze or refrigerate until ready to serve. See notes.
-Remove cover. Add 1/4 cup finely shredded Parmesan.
-Reduce heat to 375 and bake for an additional 25 minutes, until the cheese is hot, bubbling, and begins to brown. Top with chopped parsley and let it sit for 5 minutes prior to serving.