Spray your crockpot with cooking spray or use a liner. Then peel and thinly slice your potatoes. I did around 1/4-1/8 inch thick. I prefer thinner but if you don't use a mandoline it is hard to get super thin.

In a pot on the stove you are going to add the butter and melt it on medium low heat.

Once the butter is fully melted whisk in the flour and cook for 2-3 minutes, to cook the flavor off the flour.

Add in some salt, pepper, and the garlic powder. Then slowly whisk in the milk, making sure to whisk any lumps to break them up.

Once the milk has been added and the mixture is smooth, remove from the heat and add in the sour cream and the shredded cheese. Whisk again until fully incorporated.

Now you will add a single layer of potatoes on the bottom of the slow cooker. Season with salt and pepper.

Then add a bit (around 1/4) of the cheese sauce. Then repeat a potato layer, then cheese sauce, until you finish with cheese sauce.

Place around 3-4 paper towels on top of the crockpot and place the lid on. Cook on high. The paper towels will soak up the condensation to help keep the potatoes crispier.

Around the 2 hour mark I removed the lid, and tossed the paper towels. Mix lightly to adjust the potatoes for a more even cook.

Place new paper towels on top and lid.

Cook for another hour and check the potatoes. If they are close to fork tender, add on the final cheese and cook an additional 15-20 minutes. Or if the potatoes are still hard, cook longer.

Depending on size of potatoes it can take anywhere from 3-5 hours to cook your potatoes. The thinner the potatoes the less cook time it will need. Mine were done at the 4 hour mark.

When your crockpot au gratin potatoes are done, garnish with parsley flakes and serve.