Potatoes Au Gratin

That pile of sliced potatoes from Monday's post went into this yummy Au Gratin recipe. I suggest doing an hour or so of exercise before chowing down on this. It's not for the calorie or carb faint-at-heart. 

• 2 tbsp unsalted butter 
• 1 medium shallot, finely minced 
• 1 clove garlic, finely minced 
• 4 pounds Yukon gold potatoes, sliced 1/8" thick 
• 3 cups heavy cream
• 1 cup whole milk
• 4 large sprigs fresh thyme
• 2 tsp kosher salt
• 1/2 tsp ground black pepper 
• 1/3 cup grated Parmesan cheese 
• 1 cup shredded cheddar cheese

Preheat oven to 350 degrees. Melt the butter in a large Dutch oven over medium-high heat. Add the shallots and cook until softened, about 4 minutes. Add the garlic and stir for 30 seconds. Add the potatoes, cream, milk, thyme, salt and pepper and bring to a simmer. Cover, adjusting the heat as necessary to maintain a light simmer and cook until the potatoes are almost tender, about 15 minutes,

Remove and discard the thyme Sprigs. Transfer the potato mixture to a 9x13 dish and sprinkle with Parmesan and cheddar cheese. Bake until the cream has thickened and is bubbling around the sides, and the top is golden brown, about 20 minutes. Cool for 5 minutes before serving.