Start by cooking the sweet potato in a large pan of boiling water for 8–10 minutes, until the cubes are fork-tender. Scoop them out with a slotted spoon and set aside.
Melt the vegan butter in a frying pan over a medium heat. Stir in the flour and whisk for 2–3 minutes to cook it out, then add the garlic granules and season with salt and pepper.
Slowly pour in the oat milk, whisking constantly, and keep going for 5–10 minutes until the sauce is thick, smooth and glossy.
While that’s happening, cook the macaroni according to the packet instructions. Drain, reserving 50ml of the cooking water, then set both aside.
Heat the grill to medium–high.
Stir the vegan cheese into the sauce, followed by the buffalo sauce, Dijon mustard, reserved pasta water and the cooked sweet potato. Use a potato masher to gently crush the sweet potato straight into the sauce, then stir until creamy and fully combined. Taste and adjust the seasoning.
Fold the macaroni into the sauce and spoon everything into a 1-litre baking dish.
Mix the breadcrumbs with the buffalo sauce and olive oil, scatter over the top, then pop under the grill for 3–5 minutes until golden, bubbling and irresistibly crunchy. Serve straight away, while it’s gloriously hot.
