Place the potatoes in a large saucepan set over medium-high heat, then cover with cold water and season with salt. Bring to a boil and cook until the potatoes are tender, 10 minutes. Drain and place the potatoes in the bowl of a stand mixer fitted with the paddle attachment. Add the sour cream, cream cheese, pepper Jack and some salt and pepper, and mix until fluffy. Taste and adjust the seasoning as needed. Fold in the green onions and enjoy!