Preheat the oven to 220ºC, gas mark 7. Heat 1 tbsp oil in a medium high-sided casserole or heavy-based pan, then add the shallots and a little salt. Soften gently for 5 minutes.
Trim, quarter and thinly slice the beetroot. Toss in a large roasting tin with the whole garlic cloves, the remaining 1 tbsp oil and 100ml stock. Roast for 20 minutes, stirring once, until just tender and caramelising. Scatter with the walnuts and ½ the rosemary, then cook for 5 minutes more until the nuts are toasted.
Sizzle the arborio rice with the shallots for 2 minutes. Stir in the crushed garlic glove for 30 seconds, then add 500ml stock. Simmer rapidly for 5-7 minutes, stirring a couple of times, until the pan base starts to appear as you stir. Repeat with the remaining stock.
Stir in ¾ of the feta, cover and set aside for 5 minutes. Stir well to fully melt the cheese. The rice should be just al dente, creamy and flowing. Add a dash of water if needed and season to taste. Mix the dukkah and remaining rosemary. Plate up the rice, then top with the nutty beetroot, dukkah, the remaining feta and a drizzle of oil, if liked.
