How does White prove an advantage after 3...Be7 4.Ngf3 Nf6 5.e5 Nfd7 6.Bd3 c5 7.c3 b6 8.Qe2 a5 9.0-0 Ba6 10.c4 Nc6 11.cd5 Bd3 12.Qd3 Nb4?

The b6+Ba6 idea in general in the French is more typical than the modern dynamic g5 ideas. So, i would think that b6+Ba6 is more typical than Nc6+g5.

You are talking about 3...Be7 4.Ngf3 Nf6 5.e5 Nfd7 etc....I actually think that the b6+Ba6 idea played by Caruana and Nepomniatchitchi are comfortable for Black. See for example the notes by Caruana in Adams-Caruana, Dresden 2008. I also believe that Nc6+g5 is very complicated and unclear. I was surprized when i saw Ziegler putting an =+ in his notes in one game in his DVD! I know it is not that simple (McDonald for example thinks that White has a slight advantage) but i believe that Black has no particular problems.

Yes, i agree that it is to early to form any conclusions by just these moves but i said that i analysed ALL the games in megabase 2009 and the ECO reccomendations and after this work i have done  i think i am in place to form some conclusions. (Ofcourse it is impossible to put here all the analysis, that's why i wright only the conclusion). And i have a lot of experience in these lines and i know the ideas you mentioned. 

For example you should know that A.Ziegler who made a DVD on the French Defence reccomends 12.g3 against 11...Qc7 and thinks that White has a slight advantage. Ofcourse one of the big experts in this line is GM Berg who has made quite a lot of development with interesting ideas (he played a stunning ...d4 move in one of his most recent encounters. I'm sorry i cannot remember jis opponent now, but i remember that i had found a cool ...Kh8 improvement on this game). One should also study the games in chess informant in this line and the analysis there.

But i think that 12.h3 is a really nice try that is negleted. The same evaluation as my coach did after 12.h3! O-O 13.Be3! Bd7 14.Rac1 Rae8 15.Re1! (slightly better for White) is given also by GM Knaak in his annotations in megabase. So, should we say that his evaluation is not correct because we are not in place to evaluate the position at this stage? I think that it is abvious that he also has seen a lot in this line and has formed a conclusion. All i say is that White should look at this line because it is simple, with no special risks (remember the exchange sacrifices in the other main lines that Black has!), and simple to learn and play.

I'd like to share with you another funny game of mine played a couple of months ago but a game i analysed seriously only yesterday with the help of my coach. The critical notice comes only after the end of the game.

1.e3 e6 2.d4 d5 3.Nd2 Nf6!? 4.e5 Nfd7 5.Bd3 c5 6.c3 Nf6 7.Ne2 cxd4
I wanted to try the understanding of my young opponent by playing the immediate 7...f6!?, but i feared that he would find 8.Nf4 so i played the line i had prepared.
8.cxd4 f6
and now i was hoping for 9.Nf4 in which i have a great score against and i think that the claims of some members of this forum that this is a forced draw are at least funny!
9.f4?!
O.M.G.! What is that? I have never seen this and i suspected that was week and immediately tried to punish this and go out for a coffe with my friends early.
9...fxe5!
Not difficult to find. The idea is 10.fxe5? Nxd4! But the game had a course i couldn't expect at this point!
10.dxe5 Bc5?!
played with the condidence that i will dominate soon. Moskalenko gives 10...Qb6 and 10...Nc5 as slightly better for Black.
11.Nf3!
What a stupid move is Bc5! was my thoughts now. I have problems based on Ng5 themes and i discovered after the game that tha variation i was basing Bc5 was false also! 11.Nb3?! Bb6 and a5-a4 with tempo but 12.Bd2! a5 13.Bc3! a4 14.Nbd4 and again white has to be better. maybe 13...Nb4 is equal.
11...O-O!
Risky but consistened. I had calculated a nice sacrifice. Also i looked at 12.Qc2 u6 13.g4 Qb6 or Nb4!
12.Ng5 Nxe5!
12.a3 a5!
Again i wanted him to play Ng5 if he wants
13.Ng5! Ndxe5! 14.Bxh7!
Easy to calculate were 14.Nxh7? Nxd3 and Qh4+ and 14.dxe5 Bxf2+ with good play. To be honest i considered then the move played an error because now the Bh7 will be hanging, but...
14...Kh8 15.Ng3!!
And know i realised that i may be lost and i have to try hard to survive.
15...Nf7?!
A practical move.

The first defence i looked at was 15...Nd7 with the idea that ofcourse 16.Nxe6? loses to Qe7 but i failed to notice a detail. I thought that i was lost after 16.Qh5 Nf6 17.Qh4 with the threat of Bg6+ and Nh5! which removes the only defender of my king! But the beautifull 17...Ra7!! 18.Bg6+ Kg8 19.Nh5 b6!! 20.Nxf6 gxf6 and Black wins! This could be an outstanding exaple of defense if there would not be the simple 16.Bg6! Nf6 17.Nh7! My coach here has the opinion that Black may be OK. F.e. 18.Ixf8 Qxf8 20.Bd2 e5! 21.fxe5 (?) Ng4!

The seconf defense i saw was absolutely beautifull but i didn;t had tha confidence to enter it.
15...Bf2+! 16.Kf1! (16.Kd2 Nc4+ 17.Ke2 e5 or Bc5 and at least there is not the immediate threat of Qh5) 16...Qxg5! 17.fxe5 Bxg3+ 18.Kg1?? Bf2+ and the Bh7 drops. This was easy but i couldn't believe that i have something after 18.Ke2. It seems that after 18...Bf2! 19.Bc2 Bd7! 20.Kd2 which was the move i was afraid with Qh5 coming there is again a cool defence! 20...g6! 21.Bxg6 (or else Kg7) 21...Kg7! 22.Bc2 Rf4! and maybe Black is on top!

Conclusion: Imaginary defence is essential if you want to save bad French positions

Let me return to the game:

16.Nxf7 (16.Qh5 Nh6 is not clear)
16...Rxf7 17.Bg6 Rc7?
I knew this was losing but i thought that it was my best chance to win the game! After 17...Rf6 18.Qh5 Kg8 19.Qh7 Kf8 20.Nh5 i have to sac the exchange with 20...Rxg6 and i thought that this was easy for my opponent to find.
18.Qh5+ Kg8 19.Qh7+?!
This was the reason i played 17...Rc7. It is easy to miss 19.f5!! and it is natural to play this check if you thionk that the win is near.
19...Kf8 20.f5!
This is not so clear now as before but i am lost! I had some hopes based on some crazy variations but i really hoped that white could play 20.Qh8 Ke7 21.Qxg7 Kd6 22.Qh6 Qf6 and it's my turn! I was enjoying myself as i was calculationg these lines!
20...Qf6 21.Qh8?!
I couldn't be happier after this! 21.Bf4! e5 22.Nh5!! is what i saw first and tried to think that 21...Ne7 may work after 22.Bxc7 Nxg6 23.Qxg6 Qxb2 but here i missed the killing 24.Bd6+!! Bxd6 25.O-O+-. The same idea works after 22.Qh8+ Ng8. I have used this position as a tactics test for some of my ypung students!
21.Qh8? Ke7 22.Qe8?
Now the trend is on my side after 22.Bf4 e5 23.Nh5 Bxf5!
22...Kd6 and now i am clearly better!
23.Bf4+ e5 24.Rd1 Bxf5!
this move reflects my nervous condition at the time of the game. I saw that i would be also winning after 24...Nd4 but i wanted to simplify the tension
25.Nxf5+Qxf5 26.Qxc6+? bxc6 27.Bxf5 exf4 and i won this endgame by putting pressure on b2 and pushing my pawn to d3.

Beautifull game but why i say all these?
After the analysis of this game my coach asked me why i play 3...Nf6 against the Tarrasch. He said that it is known that Black is worse in the main lines after 9.exf6 Nxf6 10.Nf3 Bd6 11.O-O Qc7 (the way i play it). I was curious about what variation my coach thought that White should play to claim tha edvantage here because i had done a great amount of work in all of them! He said that 12.g3 was simple enough to claim a small advantage but he mentioned a game he had some years ago against a Soviet GM who played against him:

12.h3! O-O 13.Be3! Bd7 14.Rac1 Rae8 15.Re1! and Black has no counterplay and White by simple means is better!

I had a research on this variation and i think that Black's chances shouldn't be that bad but analysing with Rybka ECO's reccomendations and the games in the database i have the feeling that my coach is right here. White has a slight advantage and above all his play is simple and practical and Black, with no real counterplay doesn't have a simple way to play the pisition! 

So, after this nervous-breaking game and my refutation of my pet 11...Qc7 i decided to turn again to 3...Be7!  

Any thiughts?