Peel, core, and slice up a whole butternut squash into ⅓" to ¼" cubes. Make sure you remove all the seeds and the stringy parts. If you can handle microwaved foods, popping the whole squash in the microwave oven for 1-2 minutes will loosen the skin and make it easier to peel.
Then carefully wash and remove the core of each apple, and cut them into ½" pieces, with the skin on if desired (to take advantage of the natural quercetin in the peel). I like to peel them for textural purposes if bringing this to an event, like pictured in the post. The apples need to be a bit larger than the squash since they cook faster.
Preheat the oven to 400°F (205°C), then measure out the butter or oil into a bowl, then add the sugar, cinnamon and vanilla (if using) and melt everything (on the stovetop, if needed). This isn't always necessary if using coconut oil or avocado oil.
Line a baking sheet with a silicone baking mat, then pour the squash and apples on in a single layer and drizzle on the butter mixture and move everything around so that each piece is evenly coated. Alternately, toss the apples and butternut squash in a bowl with the butter, until well-coated.
Put your tray of seasoned apple and butternut squash into the preheated oven and cook for 20 minutes on the middle rack before shaking the tray to move everything around and cooking for 10-5 more minutes. Oven temperatures vary a bit, so cook the mixture until the squash is fork tender and the apples are soft but not falling apart.
Once the squash is browned and softened, smelling a bit sweet and caramelized, your squash and apples are done. Serve with whipped cream for dessert or alongside savory dishes as a sweeter holiday side.