In a large pot, melt the unsalted butter over medium heat.
Add the minced garlic and grated ginger and sauté for 1-2 minutes until fragrant.
Pour in the chicken broth and water, then stir in the soy sauce and miso paste until the miso is fully dissolved.
Bring the broth to a gentle boil.
Add the sliced shiitake mushrooms and shredded carrots to the pot and cook for 3 minutes.
Add the instant ramen noodles to the pot and cook for 3 minutes, stirring occasionally to separate the noodles.
Reduce the heat to low and stir in the heavy cream and baby spinach leaves. Cook for another 2 minutes until the spinach wilts.
In a small bowl, beat the egg lightly.
Slowly drizzle the beaten egg into the simmering broth while stirring gently to create egg ribbons.
Season the ramen with salt and freshly ground black pepper to taste.
Remove the pot from heat and stir in the toasted sesame oil.
Ladle the creamy ramen into bowls and garnish with sliced green onions.
Serve immediately.