1. In a large pot of boiling salted water, cook squash until crisp-tender, 3 minutes. With a slotted spoon, transfer to a colander to drain. Return water to a boil. Add pasta; cook according to package instructions. Reserve 1/2 cup pasta water; drain pasta and return to pot.

2. In a large nonstick skillet, heat 2 tablespoons butter over medium-high. Add squash and cook, stirring occasionally, until lightly browned in spots and tender when pierced with a knife, about 8 minutes. Add escarole and cook, stirring, until just beginning to wilt, 1 minute. Add vegetables to pot with pasta. To skillet, add 4 tablespoons butter and cook, swirling skillet occasionally, until butter is lightly browned and has a nutty aroma, about 1 minute. Drizzle over pasta and toss to combine, adding enough pasta water to create a light sauce. Season with salt and pepper. Transfer to a serving dish, top with ricotta, and serve with lemon wedges.