Start by peeling and chopping your potatoes, peeling off any knots or eyes to get the softest texture possible.
Place potatoes in a large pot, cover with cold water and bring to a boil over high heat. Add 1 tablespoon salt into the boiling water and boil until fork tender, about 15 minutes.
Drain the potatoes well into a strainer. Place the pot back on the stove over medium-low heat. Add in 1 cup of the cream and 1 tsp freshly cracked pepper then bring to a simmering boil.
Add the potatoes back into the pot over the cream, then add in one stick softened butter, mozzarella, chives, and Boursin cheese.
Use a hand mixer and whip the potatoes until smooth and creamy (or a hand masher if necessary) adding splashes more cream as you go until you reach a velvety smooth texture.
Taste and adjust by adding more salt and pepper if needed. Serve in a large bowl topped with extra pats of butter and extra chives.