Heat a 22-inch paella (large shallow pan) or a large skillet over medium-high heat and add the olive oil. Sprinkle the salt in a circle around the edge of the pan to minimize splattering.
Add the chicken and pork ribs or rabbit (if using) and cook until golden brown, about 20 minutes. Turn the meat every 5 minutes. The browned, caramelized bits that stick to the pan will give lots of flavor to the paella.
Push the meat away from the center of the pan, then add the green beans and cook for about 3 minutes.
Move the beans to the edge and add the garlic. Sauté for about 30 seconds, making sure not to burn.
Add the butter beans and sauté for about one minute. Stir gently to avoid breaking the beans.
Add the paprika and sauté for about 30 seconds, then add the tomato and saffron. Gently stir together, taking care not to break the beans.
Add 5 cups (1,200 ml) of water, then use a toothpick to check the water level. Save the toothpick for later, then add the other 4 cups (960 ml) of water. Bring to a rapid boil for about 10 minutes, and then lower to a simmer for another 15-20 minutes.
Check the water level. There should be 5 cups of liquid in the pan, which is what you need to make rice for 4 people. Check by using your toothpick; the water line should match the same mark as before. If it's higher, keep cooking; if it's lower, add a bit more water. (Paella rice varieties have about a 2.5-3:1 water/rice ratio.)
Add the rice to the pan, and stir minimally until the rice is submerged in the liquid and evenly spread. Simmer for 10 minutes, then reduce the heat and gently simmer until the broth is gone, about 8-10 minutes (depending on the variety of the rice).
At the end of the cooking time, you should hear a faint ticking or cracking coming from the bottom layer of rice. (This means that the rice is caramelizing on the bottom, making the socarrat.) Turn up the heat for about 30 seconds to encourage the socorrat to form, and stop immediately if you start to smell burning.
Remove the paella from the heat. Cover with a towel or newspapers and let it rest for 5 minutes, then serve immediately.