Nonstick cooking spray
2 tablespoons butter
½ cup all-purpose flour
2 cups milk
1 cup heavy cream
1½ cups shredded cheddar cheese
6 medium Yukon Gold potatoes, peeled and sliced very thin, about ⅛ inch
1 cup thinly sliced yellow onion
4 cloves garlic, minced
½ tablespoon minced fresh rosemary
½ tablespoon minced fresh thyme leaves
¾ tablespoon kosher salt
¼ cup grated Parmesan cheese
1 tablespoon chopped fresh parsley
Spray inside of a 6-quart slow cooker with nonstick cooking spray.
In a medium-sized sauce pot, melt butter on medium heat until it starts to bubble. Whisk in flour.
Gradually pour in milk and cream, whisking until smooth. Simmer for 2 minutes.
Whisk in cheddar cheese.
In a mixing bowl, gently, without breaking the potatoes, mix sliced potatoes, onions, garlic, rosemary, thyme and kosher salt.
In the slow cooker, arrange a layer of one-fourth of the potato mixture. Pour a cup of cheese sauce over potatoes. Repeat to make four layers.
Cover the slow cooker and cook on high heat for 4 hours.
Top with Parmesan cheese and parsley and serve.