Personally, I think the whole "You can't Burn Fat and Build Muscle at the same time" mantra, is simply rooted in old school bodybuilding methodology. When they used to say that, what they really meant was "You can't Burn Fat FAST and Build Muscle FAST!" It's either one or the other if you're in a hurry. And since competitive bodybuilders are ALWAYS in a hurry for results - they either need to pack on mass or cut fat very rapidly - you can't do both rapidly.
Over-eating, in itself, is anabolic. So just by the pure nature of it, it's MUCH easier to build muscle when you're taking in excessive calories every day.
And vice-versa, by eating less calories than you burn each day, you'll lose weight.
However, the calorie-in / calorie-out doesn't take into account the type of training you do. If you are strength-training then your body is automatically going to take calories away from your daily intake in order to repair and rebuild muscle tissue. So at a maintenance level, with strength training included, you'll actually build muscle and burn fat at the same time. Focus on super-sets and shorter rest periods to turn your strength-training into a double blast with a cardiovascular kick; and you'll speed up the process.