For the chicken stock, after separating wings, legs and main meat from chicken, add leftover bones, leek and 3 litres of cold water to a stock pot.
Bring to the boil, then simmer for between 45mins and 1 hour 30 mins.
Check that the paella pan is levelled, then pour in enough olive oil to coat the pan.
Salt the chicken meat and then fry it on high heat.
Meanwhile, snap the runner beans and chop the garlic finely.
When the chicken is ready and nice and brown, remove chicken to a separate plate. For a paella burner, turn the outer ring off and lower heat on the inner ring, then push chicken to sides of pan to stop from cooking.
Put the snapped runner beans into the pan with a small pinch of salt and fry until caramelised, then push to outsides of the pan.
Add minced garlic to the centre of the pan and fry on low heat until golden brown.
Add 1/2 teaspoon of sweet paprika and mix it all together for 4 or 5 seconds, and then add the tomato puree on top.
Re-add chicken to the pan and then pour in the chicken stock so that it reaches the top of the rivets on the pan. Turn up the heat and boil down until the broth is right below the rivets.
While waiting, wrap a pinch of saffron in some aluminium foil, and place it close to heat for 3 or 4 minutes until slightly crunchy. Place in a small bowl and break down with fingers.
Add a ladel of the stock from the paella pan to the bowl of saffron so that it infuses for a few seconds. Add the saffron water back to the pan and stir.
Add a leveled tablespoon of salt to the pan, then pour the rice into the pan, mix until the rice is evenly distributed.
Immediately set an alarm for 18 minutes. The first 5 minutes on high heat, then 5 minutes on medium heat and then 8 minutes on low heat.
For the final 30 seconds, turn the heat up again. Drizzle olive oil and place some rosemary on top. When the time is up, turn the heat off and cover the pan with a clean tea towel. Let it sit for 5 to 10 minutes before serving.