In a large skillet, cook the bacon until crisp over med-high heat. Transfer to a paper towel using a slotted spoon and drain off all but two tablespoons of fat. Return the pan to the heat and add the onions. Cook for 2 minutes and then stir in the celery. Cook the mixture until softened and then transfer to the slow cooker. Add the potatoes, stock, onion powder, garlic powder, salt and pepper to the slow cooker. Cover and cook on high for 4 hours or low for 6-7 hours.

Using a ladle, pour 2 cups of the potato/broth mixture to a blender. CAREFULLY, puree the mixture until smooth. (Cover the top of the blender with a towel, hot liquids in a blender can explode and the towel will protect you.) Pour the pureed potato mixture back into the slow cooker and stir to combine, Add the half and half, yogurt and cheese. Stir to combine. Serve topped with the reserved bacon, cheese and scallions.