This sumptuous one-dish meal is a variation on chicken pot pie, with a crust of thinly sliced potatoes in lieu of pastry and a delicious spinach filling.
For a real time saver, use leftover chicken (or a purchased roast chicken) — or you can simply poach 3 chicken breasts and cube or shred the meat.
Any kind of potato will work for the topping, but we especially like our Organic Heirloom Fingerlings for their sweet, earthy flavor.
Position a rack in the middle of the oven and preheat to 375 degrees F. Butter a 2-quart baking dish (8x10-inch) and set aside.
Bring a large pot of salted water to a boil over high heat. Add the potatoes, reduce the heat to medium, and simmer until the potatoes are almost tender, 8 to 10 minutes. Drain thoroughly and set aside.
Heat the oil in a large skillet over medium heat. When the oil is hot, add the bacon. Cook, stirring frequently, until the bacon is crisp. Remove the bacon with a slotted spatula and drain on several thicknesses of paper towels.
Add the onions to the bacon fat in the skillet and cook, stirring occasionally, until the onion is tender, about 8 minutes. Add the garlic and cook 1 minute. Raise the heat to medium-high and add the spinach, stirring until it wilts. It may be necessary to do this in batches, depending on the size of your pan. Transfer the contents of the pan to a sieve set over a bowl and let the excess liquid drain.
In another medium saucepan, melt the 2 tablespoons of butter over medium heat. Stir in the flour and cook, stirring constantly for 2 minutes. Add the chicken stock and cream and whisk to blend, cooking until the bechamel sauce has thickened, 5 to 10 minutes.
Place a layer of potatoes, overlapping slightly, in the bottom of the prepared pan. Cover with the spinach mixture, then scatter the shredded chicken and bacon over the spinach layer. Add half of the cheese, and then top with the bechamel. Finish with a slightly overlapping layer of potatoes, then top with the remaining cheese. Season with salt and freshly ground black pepper.
Place the dish on a rimmed baking sheet and bake until the potatoes are golden and tender, and the cheese has browned, 45 to 55 minutes. Serve hot.