How to Make It
In a medium saucepan, bring the stock just to a boil. Remove from the heat and add the guajillo and árbol chiles and let stand until the chiles are softened, about 20 minutes. Transfer the chiles and stock to a blender. Add the oregano and cumin and puree. Strain the broth through a fine sieve back into the saucepan.
In a large, deep skillet, heat the olive oil until shimmering. Add the kale and garlic and cook over moderately high heat, stirring often, until the kale just starts to wilt. Add the chile broth and bring to a boil. Cover partially and simmer over moderately low heat until the kale is tender and the broth is slightly reduced, about 15 minutes. Season with salt.
The chile broth can be refrigerated for up to 3 days or frozen for up to 1 month.