Warming and hearty!
Wash the kale and remove the bottom inch of stem. Chop roughly into 1-inch pieces.
In a large skillet over medium heat, sauté the bacon for 1 minute or until just barely showing color. Add the kale and stir to coat with rendered fat.
Cook about 5 minutes, stirring occasionally, until the kale begins to wilt. Add 2 cups chicken stock, lower heat to medium-low and cook for about 10 minutes, stirring occasionally.
Transfer the mixture to a blender; or blend with an immersion blender. Puree, starting on the lowest speed, until smooth. Pour into a large bowl and set aside.
In the same skillet over medium heat, heat the olive oil and cook the onions and salt about 3 minutes until the onions just barely show color. Add the chopped apples and cook, stirring occasionally, for 5 more minutes, or until the apples soften and onions are translucent. Stir in the remaining 2 cups of broth.
Transfer the mixture to the blender, again splitting into two batches if necessary. Puree until smooth. Combine the pureed apple and onion mixture with the kale mixture, and whisk to combine. If soup seems too thick, add more stock or water until it reaches the desired consistency.
To serve, reheat if necessary, and garnish with a dollop of plain yogurt or creme, and a few grinds of black pepper.
When working with hot liquids in a blender, it's wise to hold down the lid with a kitchen towel in case some liquid escapes when the motor is running. Also, fill the blender no more than halfway and puree in two batches if necessary.