Preheat the oven to 400°F and line a sheet pan with parchment paper.
In a bowl, whisk together the harissa, maple syrup, neutral oil, apple cider vinegar, and salt.
Toss the carrots in the harissa mixture until evenly coated.
Arrange the carrots in a single layer on the prepared sheet pan, leaving space between them so they roast rather than steam.
Roast for about 40 minutes, until fork-tender and caramelized.
Switch the oven to broil and cook for 4–5 minutes, watching closely, until lightly charred at the edges.
While the carrots roast, make the tahini drizzle. In a small bowl, whisk the tahini with cold water, adding the water a tablespoon at a time until smooth and creamy. Stir in the apple cider vinegar, maple syrup, and salt.
Transfer the carrots to a serving platter. Spoon the tahini over the top and scatter with pepitas.
Finish with flaky salt if desired and serve.