In a 10-inch skillet, melt butter over medium heat. Whisk in miso and garlic; cook, stirring constantly, until miso is smooth and garlic is fragrant, about 1 minute. Whisk in water and soy sauce and bring to a simmer.
Add ramen and cook, stirring occasionally, until noodles are just softened, about 3 minutes.
Add bok choy and cook, stirring occasionally, until bok choy is tender and sauce has thickened slightly to coat noodles, about 2 minutes. Remove from heat. Stir in chili crisp and brown sugar, if using.
Transfer to a large bowl. Top with the eggs and scallions, if using. Drizzle with more chili crisp, if desired.
