Gaining muscle mass but staying lean

[jenniishtar]

Hi,one problem area for me has always been that my legs are too skinny. I'm pretty much skinny all around but have that little extra belly fat that prevents my abdominal muscles from being visible. I've been working out on and off for about a year but am now getting serious about it. Currently I'm 5'1 and about 100 lbs, I train legs twice a week. My leg routines consist of mainly squats, lunges, deadlifts.. I don't have an extremely strict diet but I consume healthy meals daily. I'll have proats for breakfast, my snacks are usually fruits/ berries and nuts, a typical lunch is chicken spinach and sweet potato. After a workout I try to eat high glycemic carbs and protein. I drink a lot of water throughout the day and during exercise.
Now my question is, should I start taking a mass gainer to help put on muscle. I have a Weider mega mass 2000 but don't know how/when to take it or if I even need it. I want to be able to gain the muscle weight but I also want to be lean so my abs can start to pop. How do I grow muscle but also lose belly fat to let my abs show? I work them about 6 times a week and they were very visible when I was eating less calories, however that was stopping my legs from growing.
I apologize for the length of this question, just wanted to give all necessary details Thanks in advance!

[nacersusaf]

Before you jump into a mass gainer...

What does your diet look like currently? (In more detail)
Do you count calories/macros?
Do you use a digital scale?

From what you posted it seems like you just aren't eating enough, but a mass gainer isn't going to help you to stay lean and put on muscle at the same time; most of them are filled with garbage.