Pommes Boulangère

Quick Summary: A classic French potato casserole layered with caramelized onions and baked in a rich stock until tender and sliceable.
Source: Claire Saffitz

>> servings: 2
Preheat #oven{} to 400°F.
 
In a #skillet{}, heat @unsalted butter{3%tablespoons} and caramelize the halved and very thinly sliced @large yellow onion{2}. Set aside.
 
Halve the @garlic{1%clove} and rub a #3-quart baking dish{} with it, then coat the dish with room temperature @butter{to coat}.
 
Scrub the @fingerling potatoes{3%pounds} and slice them into 1/8-inch-thick rounds.
 
In the reserved #skillet{}, heat @unsalted butter{1%tablespoon} over medium-high heat. Add about one-third of the sliced potatoes and @fresh thyme{1%sprig}. Season lightly with @Kosher salt{} and @freshly ground black pepper{}. Cook until browned, about ~timer{5%minutes}. Scrape the potato mixture into a #large bowl{}.
 
Repeat the browning step two more times with the remaining potatoes, @unsalted butter{2%tablespoons}, and @fresh thyme{2%sprigs}, adding the cooked potatoes to the bowl each time.
 
Layer in the prepared #baking dish{}: one-third of the potatoes, half of the onions, another third of the potatoes, the remaining onions, and finally the remaining potatoes.
 
Heat the @chicken or turkey stock{4%cups} and season with @Kosher salt{}. Pour the hot stock over the assembled layers.
 
Bake for ~timer{1 hour and 20 minutes}.
 
Let rest for at least ~timer{1%hour} before serving.
 
When ready to serve, reheat in a 350°F #oven{} for ~timer{20%minutes}.