Cut the stem and root ends off the onions. Then halve the onions and cut them into thin slices. Add extra virgin olive oil and butter to a large skillet over medium heat. Add the onions, salt and sugar. Let the onions cook slowly for 15-20 minutes stirring occasionally to prevent from burning. When onions turn brown deglaze with vinegar, add kale, stir and cook for 2-3 minutes longer.
In the meantime, cook the Ravioli according to package instructions and drain, reserving 1/2 cup of the pasta cooking water.
Add the Ravioli to the skillet and gently toss to combine adding some pasta water to achieve desired consistency. Garnish with goat cheese and a turn of freshly ground black pepper and serve immediately.