Start by chopping up your tomatoes and onions into small pieces.

Next, remove the stems from your pasilla chiles and cut them into thin strips.

Throw the chiles into a large skillet along with some minced garlic cloves and a pinch of salt.

Now add onions and mix them for 2 mins.

Then add tomatoes and mix for another 2 mins.

Now add the water and bring the mixture to a simmer over medium heat, adding water as necessary to prevent it from sticking to the pan.

Keep stirring until the ingredients for another 2 mins.

Allow the mixture to cool down then add it to the blender and blend it to a smooth paste.Taste for seasoning and adjust as needed.