Place butternut squash cubes on large baking sheet. Drizzle with olive oil, then season generously with salt and pepper. Mix well.
Roast squash for 20 minutes, then flip. Continue cooking until tender and easy to mash, about 15 to 20 minutes more.
Transfer squash to food processor, then purée until smooth. Set aside.
Prepare Potatoes:
As soon as squash goes in oven, place potatoes in a large pot. Cover with two inches of cold water, as season water generously with salt.
Bring potatoes to a boil, then cook until tender. Drain.
Using potato ricer, rice potatoes over a medium bowl. Set aside.
Combine Squash and Potatoes:
When potatoes and squash are ready, heat butter and milk over medium heat (in the same pot you used for the potatoes).
When butter mixture is hot and melted together, add potatoes and squash. Cook (stirring constantly, but gently) until combined and hot.
Season mash generously with salt and pepper to taste.
Serve hot. Enjoy!
Notes
This recipe makes about 6 cups of mash, or about 12 (½ cup) servings.If you don't have a food processor or potato ricer, you can mash everything together with a potato masher.To make this side dish vegan, simply use non dairy milk (I recommend using soy milk, which has a rich texture and neutral flavor) and plant based butter.Make sure to check out the info before this recipe card for helpful tips, variations, servings suggestions, and more!