How to Make It
Light a grill. When the fire is hot, set a paella pan or medium roasting pan on the grill. Add the olive oil. Add the leek and garlic and cook, stirring, until wilted, about 2 minutes. Add the chicken and season generously with salt and pepper. Cook, turning, until beginning to brown, about 4 minutes.
Add the rice to the pan and stir to coat with oil. Add the fava beans and then the hot stock and bring to a simmer. Stir in the the saffron, shake the pan to loosen the rice and simmer for 4 minutes. Stir in the tomatoes, thyme and rosemary and season with salt and pepper. Spread the rice in an even layer and nestle the clams in the rice, hinges down. Cover the grill and cook until all the clams open and the rice is tender, 15 to 20 minutes; rotate the pan halfway through cooking. Remove the pan from the grill and cover with a kitchen towel for 5 minutes to steam, then serve.