In a large saucepan or dutch oven over medium-high heat, melt 1 tablespoon butter. Add shiitake mushrooms, salt, and pepper to taste and saute mushrooms until just softened and golden. Remove from pan and set aside.
Melt remaining 1 tablespoon butter in same pan over medium heat. Add sliced onions and slowly saute, stirring occasionally, for 15-20 minutes until onions are a deep golden caramelized brown.
Increase heat to medium-high and add serrano pepper, garlic, ginger, and miso paste. Cook 1-2 minutes until fragrant, then add broth, vinegar, and soy sauce.
Bring broth to a simmer over medium-high heat, then reduce heat to medium-low and let simmer 20 minutes.
Once broth has simmered 20 minutes, add ramen and shiitake mushrooms. Let stand 5 minutes until noodles are softened and gently break noodles apart to incorporate into broth.
Ladle ramen into bowls and top with carrot shavings, green onions, cilantro, and soft-boiled eggs. Enjoy!