Purple potatoes are vibrantly violet on the outside, and white on the inside.
1 1/2 cups milk
1 tablespoon butter
2 tablespoons flour
2/3 cup grated cheddar cheese
2 pounds purple potatoes, unpeeled and sliced thinly
1 cup sliced shallots
1 tablespoon olive oil
4 slices bacon
1/2 cup grated parmesan cheese
Salt and pepper to taste
To make the gratin sauce, place the butter into a small pan and melt. Add flour and stir to combine, cooking over medium heat for about 1 minute. Whisk in the milk and stir until thickened. Stir in cheese; when melted remove from heat. Salt and pepper to taste.
Sauté the shallots in the olive oil until slightly brown and caramelized. Remove from the pan. Add bacon and cook until cooked through but not crispy (it will get crispy later). Cut bacon into 1-inch pieces.
Grease a shallow baking dish. Add half of the sliced potatoes to the dish. Sprinkle the shallots over the potato layer. Add the remaining potato slices to the dish. Pour the gratin sauce over the top of the potatoes, spooning into any visible cracks and crevices. Top with parmesan cheese. Add the bacon over the top. Place into a preheated 350 degree oven for 40 minutes.