Preheat the oven to 350°F. Drizzle a baking pan with Olive Oil.

Cut the Tomatoes in half and place cut side down in the baking pan.

Add the quartered Onions to the pan, drizzle some more Olive Oil over everything and pop the pan in the preheated 350°F oven for about 45 minutes or until the Tomato skins start to split and char. 

Once the veg is roasted, it's time to peel the skins off the Tomatoes. There's a couple of ways that makes it easy. The first option is to place all the tomatoes into a ziploc type baggie and seal for a little bit to steam them. Then you can easily peel off the skins. Second option, use a pair of tongs, or if like me, your "asbestos" fingers to peel the skins straight out of the oven. 

Add the peeled Tomatoes, roasted Onions, Chipotle Peppers, Salt, the Juice of 2 Limes, and the Cilantro to a blender and puree for about 30 seconds or until you have the consistency you desire. Give it a taste, and adjust the seasoning if needed.

Allow to cool, then keep refrigerated in a sealed jar until ready to use.