Preheat the oven to 425ºF / 220ºC and line two baking sheets with parchment paper.
In a large bowl toss the carrots, mushrooms, shallots, olive oil, one teaspoon of salt and half a teaspoon of pepper until evenly coated.
Tip onto the baking sheets and bake until the carrots are tender and the mushrooms have browned (30-45 minutes)
In the meantime, mix together the butter, miso, garlic, soy sauce, vinegar and two tablespoons of parsley in a small bowl.
In a separate bowl toss the chopped scallions and remaining tablespoon of parsley.
As soon as the trays come out of the oven, toss with the miso butter then transfer onto a serving platter and sprinkle over the scallions and parsley.