Preheat the oven to 425 degrees . In a saucepan, bring the clam juice to a simmer over medium heat.
Preheat a large (10- to 12-inch) cast-iron skillet over medium- high heat. Add the EVOO, onion, bell pepper, garlic, 1 tsp. salt and 3/4 tsp. pepper and cook, stirring occasionally, until the onion is golden, about 5 minutes. Add the tomato paste, paprika and saffron and cook, stirring, for 1 minute.
Add the rice, stirring to coat, then stir in the wine. Bring to a boil, cooking until the liquid is reduced by half, about 2 minutes. Add the hot clam juice, stir once, then bring to a boil and cook for 5 minutes.
Add the clams; transfer the paella to the oven. Bake until the clams open (discard any that don't), about 30 minutes. Nestle the shrimp into the paella. Bake until the rice is cooked through and the shrimp are opaque, about 5 minutes. Let cool for 5 minutes before serving.