Pour your condensed Milk in a pot/dish (preferably non-stick) and add sugar to it
Now stir the mixture on medium-low flame
Once the sugar dissolves and the mixture starts to bubble add the butter and stir continuously
Add the Vanilla Essence to the mixture
In the meanwhile grease a separate tray with butter (Mixture will be poured onto this tray)
Keep stirring the mixture anywhere between 30-45 minutes until you get a caramel colour.The flame should be low
Please stir continuously and scrape any edges from the side and combine with the mixture
When the mixture doesn't stick to the dish and is of thick and sticky consistency , that's the time when the Toffee is ready. Tip: As soon as it starts to harden a bit that's the time you need to remove it from the stove
Pour the mixture on a tray and let it cool
Once it cools down, cut it into your desired shape
The more it cools, the more harder it will turn in texture
Store in a air-tight jar but I am sure it won't last long :)