I've got a Hyper-V 2012 running and need to configure that my virtual CPU are based on one socket. So the guest is seeing one socket with e.g. 4 core. I've found some tool called cpu z should do that, but is the "correct" way of doing this?
Your guest VMs will all appear as single-socket, multi-core processors (assuming you give them more than one virtual processor) unless you either reconfigure the VM manually or add enough virtual processors that you've exceeded the number of cores that your physical processors have.
If you want confirmation on how your VM appears to the running workload, I suggest coreinfo.exe:
If you want to reconfigure the VM manually, I suggest PowerShell. Look at the Set-VMProcessor cmdlet. The -MaximumCountPerNumaNode and -MaximumCountPerNumaSocket parameters should get you what you're looking for.