Makes 2 1/2 cups sauce
Preheat a broiler and position an oven rack about 6 inches from broiler unit.
On a large baking sheet, toss tomatoes and chiles with 1 tablespoon olive oil to coat. Season with 1/2 teaspoon salt and transfer to broiler. Cook until edges of tomatoes are lightly charred, 10 to 12 minutes. Remove stems from chiles, then transfer chiles (with seeds) and tomatoes to a blender and process briefly to form a chunky-smooth mixture.
In a large skillet, heat remaining olive oil and saute onion, garlic, oregano, and cumin until onions are soft, about 4 minutes. Add pureed tomato mixture and broth and cook until thickened to sauce consistency, 10 to 15 minutes. Season with remaining salt, adding more to taste if necessary. Serve warm over tamales or enchiladas.