Rinse the rice under running cold water for a few minutes so the starch washes out, then place it in a large saucepan. Pour in the hot stock, cover and simmer for 12–15 minutes, until the rice is cooked.
In a bowl, whisk together the yoghurt, egg yolk, cornflour and measured lukewarm water until smooth.
When the rice is cooked, take a ladleful of its cooking broth and add it to the cold yogurt mixture, whisking as you do so to warm it up. Then take the saucepan with the rice in it off the heat and very slowly, half a ladle at a time, spoon in the yogurt mixture, whisking all the time so it doesn’t split.
Return the soup to a medium-low heat and add the mint and half a teaspoon each of salt and white pepper. Simmer for five minutes until the soup has thickened.
Add the spinach and cook for a further five minutes, then taste to adjust the seasoning to your preference. In a separate small saucepan, melt the butter for the topping with the dried mint and aleppo pepper.
When you are ready to serve, ladle the soup into warmed bowls, drizzle a couple of teaspoons of the hot chilli-mint butter over each portion and serve immediately.