line slow cooker with liner or parchment paper, if using
spray liner (if using) or slow cooker with non-stick spray
grate both cheeses and stir together in a mixing bowl.
in a bowl or glass cup with a pouring spout, whisk together cream, garlic, onion powder and worcestershire sauce.
add one layer of thinly sliced potatoes all over bottom of slow cooker
pour ⅓ of cream mixture over potatoes
sprinkle ⅓ of grated cheese mixture over cream and potatoes
repeat all layering steps two more times beginning with potatoes and finishing with a top layer of cheese.
cover slow cooker and cook on high for 4 hours.
add salt and pepper to taste