1/4 cup shiro (white) miso
3 tbsp unsalted butter, softened at room temperature, divided
1 tbsp vegetable oil
10 oz. assorted mushrooms (we used a mix of enoki mushrooms, shiitakes, and oyster mushrooms), cleaned, tough stems removed, and cut into bite-size pieces
2 garlic cloves, crushed
1 tsp sherry vinegar
1 scallion, green parts only, thinly sliced
Preheat oven to 425 degrees F.
Drizzle mushrooms and garlic with vegetable oil, season with s&p and toss to combine. Spread mushrooms out on a rimmed baking sheet. Roast until mushrooms start to turn golden brown in places, about 10-12 minutes.
Meanwhile mix together miso and 3 tbsp butter with a wooden spoon in a small bowl. Stir until well-combined. Set aside. Heat sherry vinegar in a small sauce pan over medium heat until slightly reduced, about 15 seconds. Add miso butter and remove from heat, stirring until well-mixed. You don't want to melt the butter entirely - instead it should form a thick sauce.
Spoon miso butter onto plate. Add mushrooms and top with scallions.