Heat the olive oil and butter in a large saucepan. When the butter has melted, add the chopped garlic and onion, cover with a lid and sweat on a gentle heat for about 5 minutes, until soft but not browned. Add the chorizo sausage to the pan and cook for 3 minutes to brown around the edges and release all its juices. Stir in the rice and cook for a minute or so before adding the wine. Continue to cook for 2–3 minutes until the wine has been absorbed. Meanwhile, place the beef stock pot in a large jug and pour over 1 litre of boiling water, mixing with a spoon till the stock pot has dissolved. Continuing to cook the risotto on a gentle heat, adding a ladleful of stock at a time, stirring continuously until the previous one has been absorbed. Repeat this process until all the stock has been used up and the rice has cooked to a runny and creamy consistency. This should take about 20–25 minutes. Add the peas to the risotto in the last 5 minutes of cooking time. Finally, mix in the grated Parmesan, chopped parsley and season well with fresh black pepper. Serve the red wine risotto immediately into deep bowls with fresh rucola leaves on top.