Heat the oven to 400°F (200°C). Toss the carrot with some of the measured oil and spread on a small baking sheet. Roast for about 20 minutes, until tender with lightly browned edges; continue longer if needed.

While the carrot roasts, heat the remaining measured oil in a skillet over medium heat. Cook the onion for 6–8 minutes, until soft. Add the garlic and stir for about 1 minute, without browning it heavily.

Reserve a small splash of cool broth for the starch. Blend the drained soaked cashews, roasted carrot, onion and garlic with the remaining broth, tomato paste, nutritional yeast, lemon, vinegar, mustard, turmeric, paprika, salt and pepper until completely smooth. Scrape down and blend again if the sauce feels gritty.

Whisk the arrowroot into the reserved cool broth until smooth. Pour the blended sauce into a saucepan and warm over medium-low heat. Whisk in the slurry and cook gently for 3–5 minutes, stirring, until the sauce lightly coats a spoon. Avoid a long hard boil.

Meanwhile, cook the dry macaroni in boiling water according to its package directions, until just tender. Save a little pasta cooking water, then drain.

Fold the warm pasta into the sauce. Add a little reserved pasta water if needed for a coating that flows between the elbows. Taste and adjust the seasoning.

Spoon into bowls and add any optional herbs or crunchy topping just before serving. The sauce thickens as it stands, so bring it to the table while creamy.