1/2lb.Russet baking potatoesabout 2 medium sized or see Note 3
1cupGruyere cheesegrated, or see Note 4
Salt and freshly ground pepper
In a small saucepan, combine the 2 cloves chopped garlic with the cream. Place the thyme branches in and push down into the cream. Heat cream over low heat a few minutes, or just until warm (*do not boil!), then turn the heat off under the saucepan and allow to sit while you cook the mushrooms.
Preheat oven to 350F.
Heat oil in a large, oven-proof skillet over medium-high heat on the stovetop. Cook 1/2 of the mushrooms, stirring regularly, until most of the liquid has cooked off, but the mushrooms are still holding their shape. (If you are someone who prefers well-done mushrooms, feel free to cook longer). Remove mushrooms to a bowl and repeat with the second half of the mushrooms, cooking the same way. Remove to the same bowl.
Add a splash of cooking oil to the skillet, if dry. Add the diced onion and cook, stirring, until softened. Add the 2 cloves and stir/cook and additional 30-45 seconds. Return the mushrooms to the skillet, together with any liquid in the bowl. Stir to combine. Scatter baby spinach over the top and cook, stirring, just until the spinach wilts (you may need to do this in batches for it all to fit). *Note: The liquid from the mushrooms will help to wilt the spinach. Once the spinach is wilted and stirred in, if there is a lot of liquid in the pan, you could spoon some off, to avoid watering down the cream sauce.
Remove skillet from heat.
Wash and peel the potatoes, if desired (peeling isn't necessary though, if clean). Slice into thin rounds. Arrange the potato rounds in a single layer, slightly over-lapping, on top of the mushrooms in the skillet. Season with salt and freshly ground pepper. Top with Gruyere cheese. Slowly pour the infused cream mixture over-top, pouring all over the skillet. *You could strain out the garlic and thyme, but I like to keep it in).
Cover skillet with aluminum foil (or a lid) and cook in preheated oven for 60-75 minutes, or until the potatoes test tender when tested with the point of a knife. Remove foil and continue cooking an additional 15 minutes, or until bubbly and golden. Allow to stand a 5-10 minutes to set, then spoon out of the skillet to serving plates.
1. You could use a lighter cream, such as 10% b.f. Half and Half Cream, for a lighter dish. The sauce will be a bit runnier.2. This would be 2 standard 8oz trays of mushrooms. You can use any type of mushroom your prefer, but buying whole and slicing yourself if recommended for a chunkier layer, though not necessary.3. Alternately, you could use yellow-fleshed, Yukon potatoes, though they may require longer in the oven to soften. Be sure to test with a knife to be sure they are tender before removing the foil. If not, continue cooking covered until they test tender.4. Alternate cheese options: Jarlsberg, Emmenthal, Comte. Asiago, Fontina or Parmesan are less ideal, but will work.Be sure to read the “Ingredient and Cook's Notes" (above the recipe card!), where I share more detailed tips, variations and substitution suggestions for this recipe!