Peel and cut up potatoes and carrots. Add to boiling water. (Use enough water to cover) Cook until soft enough to mash. While they cook, chop onion and cut slices of bacon into 1/2-inch squares. Fry bacon in frying pan until half done, then add the onion and cook both until the bacon is crisp and the onion is transparent.
Drain onion and bacon on paper towels or in a colander. If you wish to save bacon grease for other cooking, place colander over a bowl to collect drippings. Mash the potatoes and carrots. Add the drained bacon and onion bits and mix well.