Specifically, which law did he break?
The Supreme Court voted 9-0 that President Obama violated the separation of powers act of the Constitution when he declared the Senate in "recess" when they were not.
Nah, they ruled President Obama's "recess appointments" made in 2012 when the Senate was holding only pro-forma sessions every three days and conducting no business, as a way of blocking the President from using the Recess Power, was unconstitutional.
Which is exactly what OldStyle stated. I dont really expect partisan asshattery from you under normal circumstances so it is rather surprising that you are purposefully blinding yourself to this fact by playing asinine semantic games.