Preheat the oven to 425F.
Wash the asparagus and snap off the bottom ends where they break easily - usually 1" - 2". Discard the ends and place asparagus spears in a ceramic roasting pan.
Melt butter and miso in the microwave for about 30 seconds. Use a spoon to drizzle over the asparagus. Grind on lots of pepper.
Bake in preheated oven for 20-25 minutes. About half way through toss the asparagus with a tongs to make sure the butter is evenly distributed and things are cooking evenly. When done, the spears will be tender when you bite them with a slight crunch.