Bring a large pot of
salted water to a boil. Cook pasta until al dente; drain, and return to pot.
Meanwhile, heat 2 tablespoons
butter in a large skillet over medium-high. Add onion and garlic;
season with salt and pepper.
Cook, stirring, until onion starts to brown, 6 to 8 minutes.
Add as much escarole to skillet as will fit; season with salt and pepper. Cook, tossing frequently, adding more escarole as room becomes available. Continue
to cook until escarole is tender, 2 to 3 minutes.
Add remaining tablespoon
butter and escarole mixture (with any pan juices) to pasta in pot; season with salt and pepper,
and toss to combine. Sprinkle with Gorgonzola, and serve immediately.