Preheat your oven to 400 degrees. Cover a cookie sheet in aluminum foil. Cover the cut sides of the butternut squash in ½ Tbs olive oil, a hefty pinch of salt, a hefty pinch of black pepper, a hefty pinch dried thyme, and a hefty pinch of rubbed sage. Rub the spices into the squash. Place the squash cut sides down onto the cookie sheet. Roast the squash in the oven for 45 minutes, until soft and you can easily stab it with a knife. Set aside once done.
While the butternut squash is roasting, boil water in a large pot. Put the sliced carrots and potatoes inside and cook until you can easily stab both the potatoes and carrots with a knife, about 25-28 minutes. Strain and set aside.
In a frying pan, add a heaping ½ cup minced onion and 2 Tbs minced garlic. Add 1 Tbs butter or ghee and 1 Tbs olive oil to the pan, mix, and cook over medium heat for 4 minutes, mixing every so often. Add 1 Tbs dried parsley, mix and cook for another 1-2 minutes.
Then, take the boiled carrots and potatoes, and the garlic onion mixture and put into a blender or food processor. Puree until smooth. Then pour the mixture into a large bowl.
Remove the skin of the butternut squash and then put the squash into a blender or food processor and puree until smooth. Mix the butternut squash puree into the potato and carrot puree.
Next, add 1 1/2 tsp salt, ½ tsp black pepper, ½ tsp rubbed sage, and ½ tsp dried thyme to the bowl and mix.
This recipe makes about 10 cups of mash total, which can serve 10 + people.