In this QGD Exchange variation, how should white deal with 6 ...Bg4?

Question

[FEN ""]
1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5 5.Bg5 Be7 6.e3 Bg4!?

The Shredder Opening Database indicates no games played with this move, and my edition of John Watson's A Strategic Chess Opening Repertoire does not cover it either (unless I'm missing a transposition of some sort), so you would expect this move to be somewhat dubious.

Yet, according to my analysis with Stockfish, not only is this move OK for Black, but White struggles to maintain an advantage without either giving up his white squared bishop or allowing Black to get his white squared bishop into the game without concessions (both important themes in this opening for White, as I understand it).

What are the main ideas for White in this line? Can White punish Black for this bold early move?

Here are a few variations that I looked at with Stockfish - I focused on what I consider "natural" moves rather than radical ideas. Is there a line I'm missing that spoils this idea for Black?

[FEN ""]

1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5 5. Bg5 Be7 6. e3 Bg4 
7. Nf3 
( 7. Qb3 Nbd7 8. Bd3 ( 8. Bf4 O-O 9. Bd3 Nb6 10. Nge2 c6 11. O-O 
{ Eval: 0.15. Black's white squared bishop is developed and he seems to 
have solved most of his problems.}  )
8... c5 9. Bxf6 Nxf6 10. dxc5 O-O 11. Nge2 Bxc5 12. O-O d4 
13. exd4 Bb6 14. Rac1 Rc8 15. h3 Be6 
{ Eval: 0.29. A pawn down, but White's isolani seems like it would 
be easy to recapture.}  )
( 7. Nge2 O-O ( 7... Nbd7 8. h3 Bf5 9. Ng3 Bg6 10. Bd3 Bxd3 
11. Qxd3 { Eval: 0.25. Exchanging white squared bishops must 
be a small concession from White.}  )
8. h3 Bxe2 9. Bxe2 Nbd7 10. O-O 
{ Eval: 0.25. This seems like the most promising line for 
White if you want a quiet position, 
but Black seems reasonably well developed.}  )
7... c6 ( 7... O-O 8. Bd3 c6 9. O-O h6 
{ Eval: 0.19. The Black white squared bishop is 
nicely developed, and the king is safe.}  )
8. Bd3 O-O 9. Qb3 ( 9. Qc2 h6 10. h3 Bxf3 11. Bxf6 Bxf6 12. gxf3 
{ Eval: 0.16. White has kingside attacking chances at the cost of a 
messed up pawn structure and dubious king safety.}  )
( 9. h3 Bh5 10. Qb3 Bxf3 11. gxf3 Qc8 12. Rg1 { Eval: 0.37: 
White attack on kingside looming, but with messed up pawn structure 
and king safety issues.}  )
9... Bxf3 10. gxf3 { Eval: 0.34. This position seems double 
edged - the White rook going to g1 looks dangerous, but the pawn 
structure is messed up and I'm not sure about the White king's safety.}   

Answer 1

There's probably no way to punish the move immediately. You'll have to play normal moves and hope that the bishop on g4 will be useless.

The only try to punish black immediately is 7. f3, but from the positional point of view it isn't a very nice move (although there might be a concrete justification) because you're weakening your king when you aren't developed. It would be very good if white was in time with e4 move, but again since he isn't completely developed, I wouldn't risk it.

I like both of the logical queen moves (Qb3 and Qc2), especially 7. Qc2, since you can play Bd3 next, fully exploiting the absence of black's bishop on b1-h7 diagonal.

For example:

[FEN ""]
1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5 5.Bg5 Be7 6.e3 Bg4 7.Qc2 O-O {And now you can play either Bd3 or h3 and Bd3.} 8.Bd3 {The position looks good to me.} (8.h3 {Challenging the bishop, which has not so many good squares.} Bh5 9.Bd3)

Answer 2

Usually white's aim in this line is to play Qc2 anyway to take away the F5 square from the black bishop. Therefore I dont think Nf3 is a great move. Its better for white to play Qc2 or Qb3 which is also thematic since blacks white squares on the queenside are now weak due to absence of the bishop.

Answer 3

A key strategic idea for white in the exchange qgd is to build a big pawn center with f2-f3 and e3-e4. Perhaps white can accelerate his normal middlegame plans by playing f2-f3 here after ...Bg4? I haven't checked this line with an engine, so unfortunately I don't have a concrete line for you.