Steps
1. Preheat the oven to 375°F (190°C).
2. Peel and thinly slice the potato, tomato, and onion.
3. In a saucepan, melt butter over medium heat and sauté the onions until translucent.
4. Add milk, salt, and pepper to the saucepan, and simmer gently for 5 minutes.
5. Layer the sliced potatoes, tomatoes, and onion mixture in a baking dish.
6. Pour the remaining milk mixture over the layers.
7. Cover the dish with foil and bake for 45 minutes.
8. Remove the foil, increase the oven temperature to 400°F (200°C), and bake for an additional 15 minutes until golden brown.
9. Let it cool slightly before serving.