Step 1

Place rack in middle of oven; preheat oven to 375°. Working in batches, cook 2 lb. fresh green beans in a large pot of boiling salted water until bright green and halfway to tenderness, about 3 minutes per batch. Drain and let cool; trim stem ends.

Step 2

Heat 1 Tbsp. extra-virgin olive oil in a large skillet over medium-high. Cook ½ lb. crimini mushrooms, sliced , without stirring, until golden brown underneath, about 2 minutes. Toss and continue to cook, tossing occasionally, until browned on both sides, about 3 minutes more. Add 2 Tbsp. unsalted butter and 2 large thyme sprigs to pan. Cook, tossing occasionally, until butter browns and mushrooms are dark brown and very tender, about 4 minutes longer. Season with kosher salt and transfer to a plate. Repeat with 2 Tbsp. unsalted butte r, salt, and remaining 1 Tbsp. extra-virgin olive oil , ½ lb. crimini mushrooms, sliced , and 2 large thyme sprigs .

Step 3

Melt remaining 2 Tbsp. unsalted butter in a large saucepan over medium-low.…