Bring a large pot of water to a boil with 2 teaspoons of salt. Drop in the stinging nettles, and cook 1 to 2 minutes until they soften. This will remove most of the sting. Drain in a colander, and rinse with cold water. Trim off any tough stems, then chop coarsely.

Heat the olive oil in a saucepan over medium-low heat, and stir in the onion. Cook until the onion has softened and turned translucent, about 5 minutes. Stir in the rice, chicken broth, and chopped nettles. Bring to a boil, then reduce heat to medium-low, cover, and simmer until the rice is tender, about 15 minutes. Puree the soup with an immersion blender, and season to taste with salt and pepper.