The cooking time for red potatoes can vary depending on their size and the desired level of tenderness. However, a general rule of thumb for boiling red potatoes for mashed potatoes is to cook them for around 15-20 minutes.

Here's a step-by-step guide on how to boil red potatoes for mashed potatoes:

  1. Wash the red potatoes thoroughly under running water and scrub any dirt or debris off the skin.

  2. Cut the potatoes into evenly sized chunks, about 1-2 inches in diameter. This will ensure that they cook evenly.

  3. Place the potato chunks in a large pot and cover with cold water. Add salt to the water, if desired.

  4. Bring the water to a boil over high heat, then reduce the heat to medium-low and let the potatoes simmer gently.

  5. Check the potatoes for doneness after about 15 minutes by inserting a fork or a knife into one of the potato chunks. If it slides in and out easily, the potatoes are done. If the potato chunks are still firm, continue cooking for another 5-10 minutes.

  6. Once the potatoes are done, drain them in a colander and return them to the pot.

  7. Mash the potatoes using a potato masher or a fork, or use a potato ricer or food mill for a smoother texture.

  8. Add butter, milk, salt, and pepper to taste, and stir well to combine.

Your mashed potatoes are now ready to serve!