Follow these detailed instructions to create a perfect Buttery Mashed Potato Casserole every time:

1. Prepare the Potatoes: Begin by thoroughly washing and scrubbing the potatoes. Whether you choose Yukon Gold or Russet, ensure they are clean of any dirt or debris. Peeling the potatoes is optional; leaving the skins on will result in a more rustic and nutritious casserole, adding fiber and a slightly different texture. If you prefer a smoother, classic mashed potato texture, peel the potatoes before proceeding. Once washed and peeled (if desired), cut the potatoes into uniform 1-2 inch chunks. This ensures even cooking. Smaller pieces cook faster and more evenly than larger chunks.
2. Boil the Potatoes: Place the cut potatoes in a large pot and cover them with cold water. The water should be about an inch above the potatoes. Adding cold water allows the potatoes to cook evenly from the inside out. Season the water generously with salt. Salting the water not only seasons the potatoes from within but also helps them cook faster and more evenly. Bring the water to a rolling boil over high heat. Once boiling, reduce the heat to medium and let the potatoes simmer gently until they are fork-tender. This usually takes about 15-20 minutes, depending on the size of the potato chunks and type of potato. You’ll know they are ready when a fork easily pierces through the center of a potato piece without resistance.
3. Drain the Potatoes: Once the potatoes are fork-tender, carefully drain them in a colander. It’s crucial to drain them thoroughly to remove excess water. Excess water can lead to watery mashed potatoes, which we want to avoid. Return the drained potatoes to the empty pot. Putting them back in the warm pot helps to steam off any remaining moisture, contributing to fluffier mashed potatoes.
4. Mash the Potatoes: Now it’s time to mash the potatoes. You can use a potato ricer, a potato masher, or even an electric hand mixer for this step. A ricer will produce the smoothest, most lump-free mashed potatoes. A potato masher will give you a slightly chunkier, more rustic texture, which some people prefer. If using an electric mixer, be careful not to overmix, as this can lead to gluey mashed potatoes. Mash the potatoes until they reach your desired consistency.
5. Melt the Butter: While the potatoes are still warm, add the butter to the pot with the mashed potatoes. The residual heat from the potatoes will help melt the butter beautifully. Allow the butter to melt completely, stirring it into the potatoes as it melts. The melted butter infuses the potatoes with rich flavor and creates a smooth, luxurious texture.
6. Warm the Milk and Cream Cheese: In a separate saucepan or microwave-safe bowl, warm the whole milk until it is heated through but not boiling. Warming the milk prevents it from cooling down the mashed potatoes and helps it incorporate smoothly. Add the softened cream cheese to the warm milk. The warmth of the milk helps the softened cream cheese melt easily. Stir continuously until the cream cheese is completely melted and the mixture is smooth and creamy. This warm milk and cream cheese mixture is the key to the casserole’s ultimate creaminess.
7. Combine Wet Ingredients with Potatoes: Pour the warm milk and cream cheese mixture into the pot with the mashed potatoes and melted butter. Stir gently to combine all the ingredients. Be careful not to overmix at this stage; gentle stirring is sufficient to incorporate the wet ingredients without making the potatoes gluey.
8. Add Flavor Enhancers: Add the minced garlic, onion powder, salt, and freshly ground black pepper to the potato mixture. Stir again to evenly distribute the seasonings. Taste the mashed potatoes at this point and adjust the seasonings to your liking. You may want to add more salt, pepper, or even a pinch of garlic powder or dried herbs like thyme or rosemary, depending on your taste preferences.
9. Preheat Oven and Prepare Casserole Dish: Preheat your oven to 375°F (190°C). While the oven is preheating, lightly grease a 9×13 inch casserole dish. Greasing the dish prevents the casserole from sticking and makes serving easier. You can use butter, cooking spray, or olive oil to grease the dish.
10. Assemble the Casserole: Transfer the mashed potato mixture into the prepared casserole dish, spreading it evenly across the bottom. You can create a smooth, even surface or leave it slightly textured for a more rustic look.
11. Bake the Casserole: Place the casserole dish in the preheated oven and bake for 20-25 minutes, or until the top is lightly golden brown and the casserole is heated through. Baking time may vary slightly depending on your oven. The goal is to heat the casserole thoroughly and lightly brown the top. If you want a more golden brown top, you can broil it for the last 1-2 minutes, but watch it closely to prevent burning.
12. Garnish and Serve: Once baked, remove the Buttery Mashed Potato Casserole from the oven and let it rest for a few minutes before serving. This allows the casserole to set slightly and makes it easier to serve. Garnish generously with fresh chopped chives or your herb of choice. The fresh herbs add a final touch of flavor and visual appeal. Serve hot and enjoy the creamy, buttery goodness of your homemade mashed potato casserole!