For me, burned food only happens in early games with new CAS sims. I always start my games with a single sim or perhaps 2 sims in a steady relationship, not with a family. One of those sims will eventually learn cooking. or learn enough advanced technology to get good meals out of the food synthesizer. By the time I have a large family with children and teens in the mix I have someone preparing perfect quality group meals way ahead of time. So essentially everyone always eats leftovers by that point. But, for that occasional new sim straight out of CAS who burns a meal, I have them trash the burnt food and either try cooking the meal again if they have time, or switch to autumn salad or a quick meal if they need to get to bed or work or class or something.