Preheat the oven to 375°F. Using a vegetable peeler, peel skin off butternut squash. Cut in half and scoop out seeds. Dice up squash into 1-inch cubes and toss into an oven proof baking dish. Toss squash with a sprinkle of salt, black pepper and a drizzle of olive oil. Roast until soft and rich in color. Longer roasting means more flavor.
In a stock pot, over a medium flame, melt butter and olive oil together. Toss in chopped onion (doesn't need to be finely chopped). Add chili flakes and cook until onions are soft and fragrant. Add roasted butternut squash, boullion cube, and pour enough water to cover squash by about 1 inch. More water means more watery soup, so if you like it thick and creamy (see above), either don't add much water, or cook it down more. Bring to a boil and then reduce heat let everything simmer together — about 15 minutes. Turn off heat and with an immersion blender, blend everything together until soup is creamy and smooth all the way through. If at this point your soup is too watery, turn the heat back on and cook it down for a while until you reach the desired consistency. If it's too thick, add water and cook a bit. Taste and add salt and pepper as needed. Serve with a drizzle of olive oil, croutons, chili flakes, or a dollop of greek yogurt.