When I hear blasphemy, I vocally turn it into a blessing, both to repair, and to correct the person. Jesus Christ...is The Name Above All Names, or, Is My Lord and Savior, or, Died for Our Sins.
Or G.D. ...is what He did to the fig tree when it bore no fruit, let that be a warning to us. Etc, you get the idea. It is a very direct way of addressing the blasphemy and the blasphemer without giving any room for conflict or retort. It always silences them. I do it all the time, automatic reaction at this point without missing a beat. It's a very successful approach.