This liquid material exhibits a sub-surface scattering effect.
The most difficult thing with this kind of shader is getting the colors to look right, and it can take a bit of fiddling and experimenting to get the exact look.
The ‘Whole Milk’ preset works well, with a couple of important adjustments. Enable Trace Reflections and increase the glossiness. Change the Scatter mode to Raytraced. This creates a nicer looking milk shader.
To make it a bit more white, adjust the colors as indicated below:
