Preheat oven to 450.
Slice onion, tomatoes, and all the peppers down the middle. Remove seeds from the poblanos, one of the jalapenos, and the serrano.*
Place those open face down on a large rimmed baking sheet. Add 6 cloves of unpeeled garlic.
Bake pan in preheated oven for 8 minutes.
Remove from oven, allow veggies to cool for a few minutes, and then add them to your blender/food processor along with the remaining ingredients. (Make sure to pop the garlic cloves out of the peel.)
Puree everything until you get an even texture. Pour into a large serving bowl and enjoy with tortilla chips, tacos, or over burrito bowls!