1) Preheat oven to 400°F. Prepare an extra-large sheet pan with parchment paper or a silicon mat.
2) Toss potatoes with 1/2 tablespoon oil, salt and pepper in a large bowl. Spread them out on a baking sheet in the upper 1/3 of oven. Roast the potatoes, stirring once or twice, until tender and browned, 15 to 20 minutes.
3) While the potatoes are cooking, tear bite-size pieces of kale off the stem and place them in a large ceramic or glass salad bowl. Add thinly sliced red onions to kale and toss.
4) As soon as potatoes are finished roasting, place hot potatoes over prepared kale and quickly cover the salad bowl with the bottom of the hot sheet pan or the lid to a skillet (even if it doesn't fit). Let covered potatoes and kale stand for about five minutes while preparing dressing.
5) Whisk oil, vinegar, garlic, honey, mustard, and salt and pepper in a small bowl. Uncover kale-potato mix and add cranberries, crumbled cheese, and salad dressing; toss to combine. Serve immediately (but it is still delicious cold).