Preheat oven to 425 degrees F. Line a baking sheet with parchment paper, set aside.
In a large mixing bowl, whisk together the flour, baking powder, salt and pepper. Add the cold cubed butter, and cut in with a pastry cutter or your fingers, until it resembles coarse crumbs the size of peas. Add the chopped bacon (reserving about 2 tablespoons for topping later on), shredded cheese, and chives (also reserving about 1 tablespoon for topping later on) and toss to evenly combine. Add the cold mashed potatoes and stir a bit to mix it all together. Pour in the heavy cream and stir until the dough just comes together, making sure not to over-mix.
Turn the dough out onto a well-floured work surface and pat or roll out into a large circle, about 3/4 of an inch thick. Cut out into 4-inch circles and arrange on the prepared baking sheet. Brush the scones with the egg wash and bake for about 20 to 25 minutes, or until golden brown. Remove from the oven and let cool slightly before topping each with a small dollop of sour cream, and a sprinkling of bacon and chives. Serve and enjoy!