Wash and peel the potatoes and add them to a large pot filled with water. Bring the water to a boil and cook for 30 minutes until tender.
Preheat the oven to 375°F and drain the potatoes. Return them to the pot and add the butter. You can cut the butter into slices to help it melt faster. Allow the butter to melt completely.
Add the heavy cream and sour cream, and stir to mix everything together.
Use a potato masher to mash the potatoes about 90% of the way. You can leave some small chunks of potato scattered throughout the pot if you like a chunkier consistency.
Stir in the salt, pepper, and bacon. Transfer the mashed potato mixture to a large baking dish and top with cheese.
Bake the mashed potato casserole uncovered for 25 minutes, or until the cheese is bubbly.
Top casserole with the optional chives after it comes out of the oven and serve.
Notes
You can store any leftover mash potatoes in an airtight container in the fridge for up to a week. Be sure to let the mashed potatoes cool to room temperature before covering with a lid. This helps prevent condensation from forming on the inside of the storage container.
Tips
Use freshly shredded cheese – It melts more smoothly and adds better flavor than pre-shredded varieties, which often contain anti-caking agents.
Make it ahead – Assemble the casserole a day in advance, cover, and refrigerate. Just bake when you’re ready to serve!
Customize the mix-ins – Add garlic salt or sautéed garlic, caramelized onions, or even a dollop of cream cheese for an extra flavor boost.