Grease a small baking dish and line with a layer of sliced potatoes.You want them to be touching enough to cover the bottom of the dish, but not directly stacked on top of one another so that they still cook evenly.
In a small bowl, mix together spinach, shallots, garlic, Greek yogurt, eggs, and a dash of salt and pepper. Spread evenly across the top of the sliced potatoes in the baking dish.
Top with another layer of potatoes.
Grate gruyère over the potatoes and another dash of salt and pepper.
Bake for 45 minutes, or until the cheese begins to brown and the potatoes have cooked throughout.