Heat a medium skillet over medium heat. (or use your grill) Add the tomatoes, shallots and serrano to the dry skillet and char on all sides, turning occasionally, 5 to 7 minutes. Transfer the charred ingredients to a blender, add the broth and process until smooth. Return the salsa to the skillet and cook over medium-high heat until the salsa turns a bright red color, 5 to 7 minutes. Season with salt and pepper. Serve warm, room temperature, or cool.