Add the sliced bacon to a frying pan over medium heat. Once the fat begins to render from the bacon add the red onion. Continue to cook, stirring occasionally, until the bacon is crispy and the onion is soft, about 10 minutes. Drain any excess fat from the pan.
While the bacon and onions are frying prepare the rest of the salad. In a large bowl whisk together the dressing ingredients until they are smooth and creamy.
Add the kale to the bowl and toss to coat. Once the bacon and onions have finished cooking let them cool for 1 minute then add them to the bowl with the kale.
Add the walnuts, sliced apple, and blue cheese to the kale and toss everything together well.
Notes
*To toast walnuts preheat your oven to 400 degrees, place the walnuts on a baking sheet and toast them for 6-8 minutes. Keep a close eye on them as they burn easily.