While the asparagus broils, make the miso-chile sauce. Heat a skillet over medium heat, then add remaining 1 tablespoon oil and heat until it thins out, about 30 seconds. Add garlic and red-pepper flakes to the pan; cook until fragrant, 30 seconds to 1 minute. Turn off the heat. Whisk in miso, sake, vinegar, mirin and sesame oil.