Cut bacon into 1-inch pieces and add the pieces to a nonstick pan.
Cook on medium heat until crisp (5-6 minutes). Keep tossing them frequently while cooking. Transfer the crispy bacon to a plate and reserve the bacon fat for the dressing.
Cut cauliflower and broccoli into small bite-sized florets. Fill a large pot with water and bring it to a boil over high heat. Once the water comes to a rolling boil, add the broccoli and cauliflower to the pot and cook for 1 minute.
Drain the broccoli and cauliflower and transfer them to a bowl filled with ice-cold water to stop cooking. Drain after a minute and set aside.
Stir mayonnaise, sour cream, lemon juice, powdered sugar, salt, and leftover bacon fat in a medium mixing bowl.
Mix cooked and cooled broccoli and cauliflower florets, red bell pepper, cranberries, walnuts, cheddar cheese, onions, and crispy bacon in a large mixing bowl.
Pour the dressing over the salad and toss well. Chill the salad for at least an hour to let the veggies soak up the dressing before serving. Serve chilled.