This winter squash side comes together easily. It takes its name from a classic French Provençal dish of vegetables baked in a shallow, round earthenware vessel called a tian. Either a 9-inch deep-dish pie plate or an 8-inch square baking dish works fine. The awkward shape and density of butternut squash makes it a challenge to prep. An easy, safe approach is to use a sharp, sturdy chef’s knife to trim off the ends, then use a vegetable peeler to remove the skin. Use the knife to cut the squash crosswise, separating the neck from the bulbous base, then halve each piece lengthwise. With a spoon, scoop out and discard the seeds from the bulb portions. Finally, with the flat side on the cutting board, slice each quarter. To prep ahead, remove the tian from the oven after the final 20 to 25 minutes of uncovered baking and hold off on adding the butter-hazelnut mixture; it will keep uncovered at room temperature for up to three hours. When ready to serve, remelt the butter-hazelnut mixture, spoon on top and bake at 450°F for 15 minutes.