Dice the potatoes coarsely and boil them until tender.
While the potatoes are boiling, render the bacon slowly. When it starts to brown add the spinach, raise the heat and evaporate all of the liquid.
Drain the potatoes and mash them with stock or heavy cream until you have the desired consistency. Fold in spinach and bacon and add cheese to taste. Season with salt and pepper.
Reheat leftovers in a microwave oven or in a double boiler.