Rinse the sweet potatoes well and boil them in a casserole with plenty of water for approximately 40 minutes. Poke them with a fork to check they are soft and remove from heat. Let them cool for a while and then peel them removing the fibres near the skin. Put them in a colander to drain well. Place them in a bowl or in the food processor and mash them. Use a non stick frying pan to brown the bacon for 2 minutes, without adding any fat, then add the milk and simmer for another 2 minutes. Add the mash and the butter. Season with salt and pepper and stir very well. Keep it warm until served.
Greek sweet potato has an ivory coloured flesh and is delicious. In the USA they produce a sweet potato variety with orange coloured flesh. If you mix the two, you will end up with both the taste and the smashing colour.