Preheat the oven to 375°F. Grease a baking dish with butter.

Wash, peel, and thinly slice the red potatoes.

In a skillet, heat olive oil over medium heat. Add minced garlic and sauté until fragrant. Add chopped spinach and cook until wilted. Season with salt and pepper.

Layer half of the potato slices in the prepared dish. Spread cooked spinach mixture over the layer. Sprinkle half of the feta cheese on top.

Repeat layering with remaining potato slices, spinach mixture, and feta cheese.

In a bowl, whisk together eggs, heavy cream, salt, and black pepper. Pour this mixture evenly over the layered potatoes.

Cover with foil and bake for 40 minutes. Remove foil and bake for an additional 20 minutes until golden and bubbly.

Let cool for 10 minutes before serving.