Soak chicos in cold water overnight. Using the same soaking water, simmer chicos over a low flame for 3 hours, until the small wrinkly kernels begin to pop, puffing up to the size of fresh kernels. Drain and set aside.
While chicos are cooking, start working on the chowder. Combine green chile, onion, potatoes, salt, pepper, and broth in a large saucepan. Bring to a boil; reduce heat and simmer 20 minutes. Strain liquid, reserving 3 cups. Mash the potatoes, chile, and onion with a large fork, or pulse in a food processor.
Melt butter over low heat in a large saucepan and add flour slowly, while whisking, to make a roux. Whisk reserved cooking liquid into the roux. Raise heat, stirring with the whisk until thickened. Add milk and continue to whisk until it comes to a simmer. Turn off heat. Add mashed mixture and blend well. Stir in chicos and serve. Garnish with cilantro.