Preheat your oven to 400 degrees Fahrenheit.
Peel the potatoes and cut into ¼ inch slices.
Place the potatoes in a pot, cover with water, and bring to a boil. Allow the potatoes to boil for 5 minutes then drain and set aside.
In a large skillet over medium-high heat, add in the olive oil. Once hot, add in the onions and sauté until lightly caramelized. Then, add in the garlic and sauté until the garlic has softened.
Melt 3 Tablespoons of the butter in a bowl in the microwave and add it to the bottom of a square baking dish (8X8 or 9X9).
Next, layer ⅓ of the potatoes on the bottom of the pan on top of the butter and season with salt and pepper. Then, add about ½ of the onions on top of this first potato layer.
After that, add another ⅓ of potatoes on top of the onions and season with salt and pepper then add the second half of onions to the dish.
Next, add the last ⅓ of potatoes to the top of the dish and season with salt and pepper. Then melt the remaining 3 Tablespoons of butter and drizzle over the top of the dish.
Then, bake in the oven for 12-15 minutes or until potatoes are ever so slightly brown and cooked until they are tender.
Finally, sprinkle with fresh parsley and serve and enjoy!