Fry the bacon in a large pan until crispy then use a slotted spoon to transfer it to a plate until ready to use. Leave about 2 tablespoons of bacon grease in the pan.
Add the chopped greens to the pan and saute them in the bacon grease until soft, 7-8 minutes.
While the greens are cooking, start the potatoes boiling. Boil the potatoes in salted water until soft. Thoroughly drain all water from the potatoes.
While the potatoes are still piping hot, add 2/3 of the butter, warm milk and cream. Use a manually masher to mash the potatoes.Add the cooked greens, bacon, green onions and white cheddar (reserving a little bacon and green onions for garnish). Stir to combine. Add the salt and pepper. Taste and add more salt according to preference.
Spoon into a serving bowl, make a small well in the center and add the remaining 1/3 butter in the well. Garnish with the reserved bacon and green onions. Serve immediately.