Remove the stem of each dried chile. Shake out as many of the seeds as possible. (Make sure you are wearing gloves, and avoid touching your eyes/face).
Heat your skillet on medium heat. Place your dried chiles on the skillet, pressing them down to toast them slightly on each side (10-15 seconds). You don't want to burn them or it will result in bitter sauce.
Add your chiles to a small saucepan, add water (just enough to cover). Bring to a boil, turn off the heat. Allow them to sit for up to 10 minutes to rehydrate.
Remove the chiles from the soaking water and place them in a blender. Add just under two cups of the soaking liquid. (If your soaking liquid is bitter then discard and add regular water).
Puree for 1 1/2 to 2 minutes. Pour through a fine mesh strainer into a skillet with the olive oil. Bring the sauce to a low simmer, add your salt, and any additional optional ingredients.
Brown sugar will tone down the spice, while cocoa/cacao will compliment the spicy sauce. Consider adding a pinch of any of the optional ingredients or more based on your preference.
Skim off the foam as the sauce simmers, then remove from the heat and store in a glass jar. Refrigerate and use within one week.