Preheat outdoor grill or oven to medium-high heat (400°F – 450°F).
In a large cast iron skillet, add tomatoes, garlic, and rosemary. Toss in olive oil and season with salt and pepper. Cook on medium-high heat with lid closed until tomatoes are blistered, garlic is fork tender and the backyard smells good enough to eat – about 15 minutes!
Open grill and work from grill or move skillet to stovetop. First, remove and discard large pieces of rosemary. Next, add tomato paste to skillet, stirring continually until heated through, about 3 minutes. Reduce grill temperature to low and add onions. Sauté for 10 minutes or until onions are translucent. Add stock, orange juice and zest to deglaze the pan, lifting the caramelized tomato bits from the bottom. Add remaining ingredients to pan, stirring to thoroughly incorporate. Then place lid on pan and add top to grill allowing contents to cook until reduced by half, about 15 to 20 minutes.
For smooth sauce, puree with a stick blender or pour into a blender and then add back to skillet.
Taste, then season accordingly. Serve with your favorite BBQ dishes or preserve per canning instructions below. Please note that the process time for jars in a water canner is 20 minutes, adjusting for altitude.