Peel and chop the potatoes and pumpkin into evenly sized chunks. This ensures even cooking.
Place the potatoes and pumpkin chunks in a large pot of salted water. Bring to a boil and simmer until both the potatoes and pumpkin are tender when pierced with a fork (usually around 15-20 minutes).
Drain the cooked potatoes and pumpkin well in a colander.
Return the drained potatoes and pumpkin to the pot. Add butter and start mashing with a potato masher. Gradually add milk as you mash until you reach your desired consistency.
Season the mash with salt and pepper to taste. Adjust the seasoning according to your preferences.
If desired, garnish the pumpkin-potato mash with chopped fresh herbs like parsley or chives. This adds a burst of freshness and color.
Serve the pumpkin-potato mash hot as a side dish. It pairs well with roasted meats, poultry, or as part of a Thanksgiving or holiday meal.