Prepare the Sweet Potatoes: Preheat your oven to 375°F (190°C).

Peel and cut the sweet potatoes into cubes.

Boil the sweet potato cubes in salted water until tender, about 10-15 minutes. Drain and set aside.

Sauté the Spinach: Heat a little olive oil in a large pan over medium heat.

Add the chopped onion and sauté until translucent.

Add the minced garlic and cook for another minute.

Add the chopped spinach and cook until wilted. Season with salt, pepper, and dried thyme (if using). Remove from heat.

Make the Egg Mixture: In a large bowl, beat the eggs.

Add the milk (if using) and mix well.

Season with a pinch of salt and pepper.

Assemble the Casserole: In a large baking dish, spread the boiled sweet potato cubes evenly.

Add the sautéed spinach and onion mixture on top of the sweet potatoes.

Pour the egg mixture over the vegetables.

Sprinkle the shredded cheese evenly over the top.

Bake: Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and golden brown, and the eggs are set.