Chop 2 cloves garlic and cut 1 medium onion into fine strips. Combine in a large bowl with 300 ml white wine and 1 teaspoon saffron threads. Stir gently for 1-2 minutes to help dissolve the saffron.
Rinse the 1 kg fresh mussels under cold water. Discard any that are already open or don't close when gently tapped. Add the tightly closed mussels to the wine mixture.
Heat 2 tablespoons olive oil in a large saucepan over high heat. Add the mussels and wine mixture, cover, reduce heat to medium, and simmer for 10 minutes until all mussels have opened.
Season the cooking liquid with salt and pepper to taste. Serve the mussels in bowls with the cooking liquid.