Peel the potatoes (if desired), rinse them, and cut them into 1-inch chunks.
Place the potatoes in a large pot, along with about 2 teaspoons of the salt, and cover with cold water.
Cover the pot and place it over medium-high heat.
When the water comes to a boil, remove the lid and turn it down to a simmer.
Simmer the potatoes until the tip of a sharp knife easily slips in and back out (approx. 5 to 10 minutes).
Drain the potatoes into a colander, then place them back in the pot, along with the butter, over low heat.
Mash the potatoes to your desired consistency.
Heat the cream and milk until steamy (in the microwave or in a small pot over medium-low heat).
Add the hot milk and cream to the pot, along with the greens, scallions, cheese, remaining ½ teaspoon of salt, and pepper.
Fold everything together, continuing to cook until the greens reach the desired tenderness.