Remove and discard heads from shrimps. With a small knife, make an incision on the back of shrimp and with the tip of the knife, remove veins.
In a saucepan over medium heat, combine guajillo peppers, arbol peppers, tomatoes, onion, whole garlic, and salt.
Add enough water to cover. Cook for about 7 to 10 minutes or until softened.
In blender or food processor, process with about 1 cup of the liquid until well-blended and smooth.
In a wide pan over high heat, heat olive oil and butter.
Add minced garlic and cook, stirring regularly, for about 20 to 30 seconds or until aromatic.
Add the shrimps and cook, stirring regularly, until color begins to change to pink.
Add sauce and bring to a boil. Continue to cook until the shrimps are cooked through and sauce is reduced.
Season with salt to taste. Serve hot.