I had half a pound of fresh kale leftover from some tomato and kale soup so I thought I'd use it up. I halved the recipe and used a small granny smith, and it came out perfectly! I used horseradish mustard because that's what I had, but it pairs well with the strong cider vinegar. I grew up eating kale cooked with cider vinegar, sugar and salt, so maybe I liked this because I knew how it would taste? The apple did a great job of sweetening and tenderizing the kale leaves. I will def. whip this up again since it took one pot, a knife and 10 minutes.