How to Make It
In a large bowl, cover the rinsed arborio rice with 2 inches of hot water. Add 2 tablespoons of kosher salt and stir thoroughly to dissolve. Let the rice soak for 40 minutes, then drain.
Meanwhile, in a large saucepan, bring 1 cup of water to a boil with the garlic halves. Add the mussels, cover and cook over high heat, shaking the pan vigorously a few times, until the mussels open, about 4 minutes. Discard any mussel shells that do not open. Transfer the mussels to a medium bowl. Pour the mussel cooking liquid into a heatproof measuring cup and measure out 2 cups; add water if necessary. Remove the mussels from their shells and transfer to a bowl.
In a large, deep skillet, heat the olive oil. Add the diced onion and cook over moderate heat, stirring occasionally, until softened, about 8 minutes. Crumble in the saffron threads and stir in the dried currants, cinnamon stick and allspice. Add the squid and cook, stirring, until it begins to curl, about 1 minute. Add the soaked and drained rice and cook over moderately high heat, stirring, until the rice starts to stick together, about 3 minutes. Stir in the mussels, the reserved 2 cups of liquid and 1/2 teaspoon of salt. Cover and cook over moderate heat for 12 minutes. Stir in the chopped scallions.
Cover the mussel-and-squid pilaf with a clean kitchen towel, then cover with the lid and cook over low heat for 10 minutes without peeking. Remove the pilaf from the heat and keep it in a warm place, covered, for 45 minutes. Stir in the dill, discard the cinnamon stick and serve.