Look up arduino reflow oven.
there are loads of people building PID controlled ovens for SMD electronics soldering and other are using the arduino to control cooking.
the same principle can be adopted for heating liquids.
you will need to download the PID library, but any of the available sketches will provide what you desire.
im currently working on a test oven at work which is using a sketch i found through adafruits site.
you will need heavy relays/SCRs or even contactors to control your heating elements, look at connecting relays to arduinos.
you might want to consider stirring the liquid to get an even heat, this is normal in industrial applications
the rest should be childs play