Preheat oven to 350 degrees F. Slice potatoes very thinly.
Add butter to a large skillet over medium low heat, When melted, add diced onion. Cook for 3 minutes, stirring occasionally. Add cream cheese to the pan and stir to melt. Pour in cream and milk, stirring to combine. Season with plenty of salt and pepper, then add chopped herbs.
Place potatoes in a buttered baking dish. Pour contents of skillet over the top. Top with parmesan cheese.
Bake for 45 minutes, or until bubbly. Allow potatoes to sit 15 minutes before serving.