In a medium (10-inch) skillet over medium heat, toast the arbol chiles until they are noticeably darker and very aromatic, about 1 1/2 minutes. Cool, then crumble into small pieces. Heat the butter in the skillet over medium heat, add the garlic and stir for a minute. Stir in the chile pieces, pepper, oregano and broth, raise the temperature to medium-high and boil until the mixture has reduced to just a few tablespoons and is noticeably thicker, about 8 minutes. Add the shrimp and stir until the pieces are nearly cooked through, about 4 minutes (there should be just a hint of pink at the center). Remove from the heat, taste and season with salt, usually 1/2 teaspoon. Lightly oil the tortillas, lay them by pairs on a griddle or skillet over medium heat, flipping to warm through. Top each pair with a portion of the cheese and let melt, then top with a hefty amount of the filling and serve.