Cut the core out from tomatoes. On a preheated comal or griddle, dry roast the tomatoes and garlic. Remove the garlic after 15 minutes, set aside.

Roast the tomatoes for 6-7 more minutes, turning as needed.

Once garlic cools, remove the skins and transfer to the molcajete. Add 1/2 teaspoon of of kosher salt. Grind down until you have a paste.

Gradually grind down the fresh serranos with the garlic. Remove the skins from tomatoes and little by little, grindthem in to the molcajete. Add lime juice and salt to taste. Before serving top with onion and cilantro.