I hate the Feedback Sandwich. Hate, Hate, Hate it.
If aren't familiar with it, this is the technique where you say something nice, offer a criticism, and then end with something nice. The idea is that it makes the criticism easier to take because we cushion the blow with some positive comments.
This is one of the worst, if not THE worst, management techniques ever. Here is why:
You have given the employee 3 pieces of feedback at once - it is impossible to know which one she heard. Don't fool yourself into thinking she heard all 3, humans rarely work like that.
You have confused the employee. Are they doing well or do they need to improve? He may hear "I just need to get better at this one thing" or he may hear "I'm doing great in 2 areas, so the one area I'm not good at is fine".
You've damaged positive feedback in the future. If you give the Feedback Sandwich often, it will dilute the message. At some point when you offer positive feedback, the employee won't hear it because they are waiting for the other shoe to drop.
It really is simple. One piece of feedback at a time. If you are giving the right proportion of positive to negative feedback, then you don't need to cushion the blow using some contrived technique.