To build muscle with minimal fat gains, start by eating no more than 5 - 10 % more calories than your maintenance level. (kingofthegym.com)
But not only is this muscle mass, it's lean muscle, meaning minimal fat gains hence the term «Lean» gains. (fitmole.org)
Here is a list of facts that can really help in handling the controversy around carbohydrates consumption and allow you to gain muscle with minimal fat percentage. (fitnessandpower.com)