Spray the inside of a slow cooker with cooking spray. [I used a 6 quart oval]
Wash and pat dry the potatoes removing any blemishes.
Toss with the olive oil and garlic salt then arrange in the bottom of the slow cooker insert.
Cover tightly and cook on high for 3-4 hours or until fork tender. [On low 6-8 hours]
Melt the butter in a small saucepan and add the chopped rosemary and minced garlic. Simmer gently for 5 minutes.
Remove the cooked potatoes from the slow cooker and drizzle with the rosemary garlic butter.
Sprinkle with grated Parmesan cheese and serve.