How would I make a circuit / do the electronics to make a motor run at variable speeds?

[Jodie Gibson]

I am a product design student, making an automatic stirring device for my final year project. I am currently at the stage of doing the electronics and want the stirrer to stir food/ sauce at variable speeds. These speed settings would be slow, medium and fast and running at speeds of approx 15 rpm, 30rpm and 60rpm. Any help with how I would go about doing this would be greatly appreciated. Thanks.