Preheat your oven to 400 degrees fahrenheit.

Using a mandolin or a sharp knife, slice your unpeeled, washed potatoes into disks, about ⅛ inch thick. Cover and set aside

In a skillet over medium high heat, melt your butter and saute your onion for about 3 minutes, until they become transparent. Add in your garlic and saute for an additional minute. Remove the pan from heat and add in your olive oil, salt, and pepper.

Pour your butter mixture into a large bowl and add in your sliced potatoes, toss to coat evenly. Once the potatoes are evenly coated in your butter mixture, add them back into the skillet.

You are going to layer the potatoes in the skillet, overlapping each one about halfway, in a circular pattern until the bottom is covered. Start again on the next layer and repeat until all the potato slices are used. Pour any remaining butter mixture over the top of the top of the potatoes.

Bake your galette until the potatoes are tender and golden, about 60-70 minutes. Once they are finished baking, remove the skillet from the oven and allow it to cool for about 15-20 minutes before removing from the skillet.