Preheat your oven to 400 degrees Fahrenheit. This will ensure the mashed potatoes bake evenly and develop a lovely golden crust on top.
Grease a 13 by 9-inch baking dish with a little butter or cooking spray. This step is important to prevent the potatoes from sticking.
Place the prepared potatoes in a large pot and cover them with water until an inch or two above the potatoes. This will help cook them evenly.
Bring the water to a boil over medium-high heat, then reduce the heat to medium-low. Allow the potatoes to simmer until they’re very tender when pierced with a fork, which should take about 15 to 25 minutes.
While the potatoes are cooking, melt the butter in a small saucepan over medium heat. Add the minced garlic and sauté for 30 to 60 seconds until fragrant. This will help to mellow the harshness of the garlic flavor.
Once the potatoes are tender, drain them and return them to the pot. Mash the potatoes well using a potato masher, or for a creamier texture, pass them through a potato ricer or food mill.
Add the melted butter and garlic mixture to the mashed potatoes, along with the milk, mozzarella, 3/4 cup of parmesan, and 2 tablespoons of chopped parsley. Stir until everything is combined and creamy. If needed, thin with more milk to reach your desired consistency.
Season the mashed potatoes with salt to taste. This is crucial to bring out all the flavors!
Pour the creamy potato mixture into the prepared baking dish and spread it out into an even layer. Then, sprinkle the remaining 1/4 cup of parmesan cheese evenly over the top.
Bake in the preheated oven for about 20 minutes. For an even more golden and crispy top, move the dish closer to the broiler for the last 2 to 3 minutes of cooking. Keep an eye on it to avoid burning!
Once the top is beautifully browned, remove it from the oven and garnish with an additional 1/2 tablespoon of chopped parsley before serving warm. Enjoy!
