Stem and seed the guajillo chiles. Toast them on a pre-heated comal or skillet, set over medium heat, for about 1 to 2 minutes per side until they are toasted, but not burnt. Place the chiles in a saucepan, add enough water to cover them, and bring to a simmer over medium heat. Simmer for 12 to 15 minutes until the chiles are plumped up and rehydrated.