Preheat oven to 200ºC/180ºC fan/gas 6. Sprinkle the saffron threads into a small heatproof glass or bowl and pour over 2 tablespoons of boiling water. Set aside to infuse.
Add the oil to a large heavy based heatproof casserole and set over a medium high heat. When it is hot, add the chorizo, onions and peppers and fry together for 10 minutes, stirring frequently until they are a little coloured at the edges.
Reduce the heat a little before stirring through the garlic and rice. Fry for a couple of minutes, making sure all the rice grains are well coated in the juices. Pour in the stock, and saffron, along with its soaking water, stirring well to mix. Season with a little salt and freshly ground black pepper, cover with a tight fitting lid or snuggly tucked piece of foil and bake in the oven for 25 minutes.
Blanch the Tenderstem in a pan of boiling water for 2 minutes. Drain well.
Remove the paella from the oven, stir through the Tenderstem and prawns and most of the parsley, recover and return to the oven for a further 10-15 minutes, until the prawns are pink and cooked and the Tenderstem cooked but with a little bite. Serve immediately, with a little extra parsley scattered on top and lemon wedges to squeeze over.
Cooks tip: Replace the prawns with an equal quantity of leftover roast chicken for an easy Monday night supper.
Recipe courtesy of Tenderstem Broccoli