It sounds to me like you're trying to unlock the aspiration. I would recommend eating 3 sandwiches with as few interruptions as possible, and as quickly as possible. Don't wait for your Sim to get hungry. I've had several Sims who made an 8-serving platter of grilled cheese, ate all 8 sandwiches without eating anything else, and still did not unlock the Grilled Cheese aspiration, so I'm fairly sure there is a time limit involved. On the other hand, I just had a Sim eat 3 sandwiches in a row and unlock the aspiration, so it is working. The only interruption was washing the dishes after the second sandwich.