Heat 1.5 tbsp butter in a pan over medium-high. Sauté Portobellos 5–6 mins until softened and lightly browned. Set aside.
In same pan, heat olive oil + 1 tbsp butter. Cook onion 3–4 mins until soft, add garlic 1 min. Pour in wine, simmer 2 mins until alcohol evaporates.
Add Arborio rice, stir until glossy and slightly translucent. Mix in miso. Add stock 1 cup at a time, stirring frequently until creamy but slightly firm in the center (14–16 mins).
Stir in Portobellos, cream, and final ladle of stock. Cook 2 mins, remove from heat, fold in parmesan. Keep slightly loose; it will thicken.
Melt remaining butter in a pan. Add quartered mushrooms and garlic, cook 5–6 mins until golden and crispy at edges. Season.
Spoon risotto into bowls, top with golden button mushrooms, chives, and extra parmesan.
