Bring broth, saffron, if using, and 1 1/4 cups water to a simmer in a small saucepan over medium heat. Add clams, cover, and simmer until clams open, 3–5 minutes; transfer clams to a small bowl (discard any that do not open). Set broth and clams aside.

Heat oil in a 12-inch heavy skillet over medium heat; add chorizo and cook until chorizo just starts to render and oil turns red, 1–2 minutes. Using a slotted spoon, transfer to a small bowl.

Place onion in skillet. Stir often until onion begins to soften, about 3 minutes. Add garlic and paprika; stir constantly until paprika is caramelized, about 3 minutes.

Stir in rice; season lightly with salt and pepper. Cook, stirring constantly, until rice is lightly toasted, about 2 minutes. Add wine; stir constantly until liquid is absorbed, about 1 minute. Stir in broth and red pepper. Simmer (do not stir), rotating skillet often for even cooking, until liquid is almost absorbed and rice is tender, 20–23 minutes. Add peas, chorizo, and clams with juices, tucking clams into rice. Increase heat to medium-high. Cook until clams are heated through and rice along bottom of pan is slightly crisp, about 2 minutes.