Peel and wash the potatoes and parsnips, then cut into small 1- to 2-inch chunks. Place the root veggies into a large pot and fill with enough cold water to cover the potatoes and parsnips by one inch, then salt with around two teaspoons of salt.
Cover the pot and bring to a boil over high heat, then reduce the heat to medium and cook until the potatoes and parsnips are soft and you can easily insert a fork in them. Drain well in a colander.
While the potatoes and parsnips cook, melt the butter in a small pan over medium heat. When the butter begins to bubble and foam, lower the heat to medium-low and stir the butter occasionally, monitoring carefully so that the butter does not burn. Add the minced garlic. The butter will turn a deep caramel color and browned bits will accumulate in the bottom of the pan. Remove from heat.
Add about half of the garlic browned-butter to the potatoes, along with the cream cheese and creamy horseradish and mash or beat with a potato masher or electric mixer. Taste the mash and add salt (1/2 teaspoon at a time, if necessary) and the 1/4 teaspoon pepper and stir.
Serve the mashed potatoes either individually plated or family style with the remaining garlic browned butter for drizzling over the top of the potatoes. Garnish with chopped chives, green onions, or parsley, if desired.
