Heat oven to 400ºF.For the roasted carrots:Rinse carrots (no need to peel!) thoroughly and pat dry. Slice into 1-inch pieces and spread on a rimmed sheet pan. Drizzle with olive oil and sprinkle with salt, tossing until well-coated. Roast for 1 hour or until fork-tender.  For the roasted cauliflower:Cut head of cauliflower into florets with cauliflower stem. Spread cauliflower on a rimmed sheet pan. Drizzle with olive oil and sprinkle with salt, tossing until well-coated. Roast for 45 minutes or until fork-tender.  For the roasted beets:Line a baking pan with aluminum foil. Rinse beets thoroughly and pat dry. Rub beets with olive oil and sprinkle with salt. Place beets in a baking ban and cover with aluminum foil. Roast in the oven for 50–60 minutes. Set the beets aside to cool for several minutes, but still warm to the touch. Peel off the outer skin and cut the beets into quarters.  For the roasted butternut squash:Line a rimmed sheet pan with aluminum foil. Cut butternut in half and scoop out the seeds. Drizzle the cut sides with olive oil and sprinkle with salt. Place butternut cut side down on the sheet pan. Roast in the oven for 50–60 minutes or until fork-tender. Set aside to cool for several minutes, but still warm to the touch. Cut off the stem and peel the outer skin of the butternut.  To prepare the vegetable mash:While your vegetable of choice is roasting, heat olive oil in a small skillet. Add onion and garlic, sprinkle with salt, and cook until translucent. Set aside. Add roasted vegetable, butter, half-and-half and sautéed onion and garlic into a food processor. Process until smooth and creamy. Add more half-and-half a tablespoon at a time if needed. Sprinkle with salt to taste and serve.