Braised Kale With Caramelized Onions

I have been eating a lot of kale lately and I found this recipe on the Peta website. I liked it a lot, but I would recommend cooking it down just a wee bit longer.

8 cups torn and stemmed kale pieces, firmly packed
1 Tbsp. olive oil
2 cups thinly sliced onions
1 tsp. salt
1/2 tsp. ground black pepper
1/2 tsp. red pepper flakes
2 Tbsp. minced garlic
2 cups vegetable stock
1 tsp. cider vinegar

• In 2 batches, blanch the kale for 2 minutes in a 6- to 8-quart pot of boiling salted water. Transfer with tongs to a colander and drain well.
• Heat the oil in a large skillet over medium heat. Add the onions, salt, pepper, and red pepper flakes and cook until the onions are golden brown, stirring frequently.
• Add the garlic, kale, and stock and cook, stirring occasionally, for 8 to 10 minutes, or until tender.
• Add the cider vinegar in the last minute of cooking, then remove from the heat. Serve immediately.