Combine sugar, condensed milk and margarine in a large, deep plastic (the biggest) bowl.
Microwave on HIGH for 2 minutes until the margarine has melted. Stir well to combine melted ingredients.
Microwave for another 10 minutes on HIGH. Stir once after 5 minutes.
When mixture is a light caramel colour add vanilla essence.
Stir very well and pour into a lightly greased flat container to set.
When slightly cool cut into squares and cool further.