Warm a large pan on a medium heat for 1 min, then add the peanuts to the dry pan. Toast for 2-3 mins till golden and nutty. Tip out into a bowl. Trim the courgette, then halve and thickly slice it. Halve the red pepper and scoop out the seeds and white pith. Roughly chop it.
Scoop the thick coconut cream out of the tin of the coconut milk and add it to the pan (keep the thin coconut water in the tin for later). Fry the coconut cream in the pan for 5-6 mins, stirring every so often, till it cracks and the oil separates from the solids. It should look oily, with the solids looking like yogurt.
While the cream fries, scrub the new potatoes and halve or quarter them so they are all roughly the same size.
Stir 1 tbsp each Thai red curry paste and tamarind paste into the cracked coconut milk and fry for a further 3 mins. Trim the green stalk off the Florence red onion (you can keep it for stir-fries), then peel and thickly slice the onion into around 8-10 wedges.
Stir the potatoes, red onion, courgette and red pepper into the fried curry paste. Cook, stirring, for 5 mins.
While the veg fry, roughly chop the peanuts. Stir the peanuts into the pan. Pour in the remaining coconut liquid, then top the pan up with 250ml boiling water. Cover and simmer for 10 mins.
Tip the rice into a small pan and pour in 300ml boiling water. Add a pinch of salt, cover and bring to the boil, then turn the heat down and simmer for 8 mins till all the water has been absorbed. Take the rice off the heat and steam in the pan, lid on, for 3-5 mins to finish cooking the rice.
While the curry and rice simmer, trim the woody ends off the French beans. When the curry has cooked for 10 mins, stir the French beans into the curry and gently simmer, without the lid on, for 5 mins till just tender. Stir in the baby leaf spinach to just wilt it.
Taste the massaman curry and add a pinch of salt if you think it needs it. Fluff the rice with a fork and spoon onto warm plates. Top with the curry and tear over some Thai basil leaves to serve.