Leaving the root end attached, peel the onion and cut into 1" sections.
Toss the cut onion and carrots with 2 Tbsp melted butter, and a hearty amount of salt and pepper.
Bake on an unlined baking sheet for 20 minutes, then shuffle the pieces/turn them over, and bake for another 20 minutes, or until the carrots are fork tender. If the onions start blackening, that's ok! When you remove them from the oven, remove the roots.
When the vegetables are done roasting, melt the remaining 2 Tbsp butter in a heavy pot over medium heat.
Remove from heat, and add the vegetables, miso, and 2 cups of broth. Using an immersion blender, or a normal blender (in batches!), blend until completely smooth, and return to heat.
Add more vegetable stock to reach your desired consistency, heat until the soup comes to a boil, then serve with sliced green onions.
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/roasted-carrot-miso-soup/