Line a cast iron skillet with aluminum foil and heat over high until it's very hot.
Add 2 cloves of garlic, 1 serrano pepper, 1/4 white onion, and 4 medium Roma tomatoes to the heated pan, flipping over each ingredient every couple of minutes to char each side.
After about 4-5 minutes, remove the 2 cloves of garlic and set on a plate to cool.
After about 5-6 minutes, remove 1 serrano pepper and set aside with garlic.
After about 8-10 minutes, remove the 1/4 white onion and 4 medium Roma tomatoes and set aside to cool.
Once the garlic has cooled, peel it.
Add the peeled 2 cloves of garlic, 1 serrano pepper, 1/4 white onion, 4 medium Roma tomatoes, 1 tsp kosher salt, the juice of 1/2 lime, and 1/4 cup cilantro (packed with the stems and all) into a blender.
Blend on the lowest setting or pulse until everything is combined. There should still be some small chunks of tomatoes to reach the right consistency.
Taste and add more salt if desired.
Serve with tortilla chips.