Preheat oven to 375 degrees.

Set a 14-inch paella pan or a 14-inch ovenproof saute pan over medium-high heat and add 2 tablespoons olive oil. Season shrimp with 2 teaspoons pimenton and 1/2 teaspoon salt. Once oil is hot, sear shrimp, about 1 minute per side. Remove shrimp from pan and set aside. Add remaining olive oil and chorizo to pan and sear, stirring occasionally, until sausage is nicely browned, 1 to 3 minutes.

Add onions, bell peppers, garlic, and saffron to pan and saute, stirring often, until lightly caramelized, 6 to 7 minutes. Add rice and cook, stirring, 3 minutes. Season with remaining salt and pimenton. Add stock to pan, bring to a boil, reduce heat to a simmer, and cook, undisturbed, until rice is no longer soupy but some liquid still remains, 5 to 6 minutes. Give rice a quick stir, then add clams with their opening edges facing up. Reduce heat to low and continue to simmer for 5 minutes. Add peas, mussels (again, opening edges facing up), and shrimp to pan and continue to cook, undisturbed, 10 minutes.

Transfer pan to oven and cook until clams and mussels have opened, liquid is mostly absorbed, and rice is almost cooked through, about 10 minutes.

Remove paella from oven and cover with foil. Let sit for another 10 minutes before serving. (The rice will continue to cook and absorb liquid as it sits.) Serve garnished with parsley.

Cook's Note: There are many regional variations of this well-known Spanish dish, but some things always remain the same: using short-grain rice, a flavorful broth, saffron, and then cooking the rice just right for the perfect texture. Although we give a suggested cook time below, stove tops and ovens do vary, so take the time to practice and perfect your paella. Be patient and have fun. Of course, a paella pan is ideal, but if you don't have one, not to worry: Simply use a 14-inch ovenproof saute pan.