Line rectangular pan with parchment paper and butter it.
Place a heavy bottomed skillet over medium flame, add butter and brown sugar.
Add milk, vanilla essence and condensed milk.
When the butter dissolves, keep a timer for 15 minutes and keep stirring. This is absolutely crucial as the caramel might get burned if you leave it on the flame.
Switch off the flame after 15 minutes and keep stirring for further 10 minutes. It will start thickening.
Transfer to the lined pan and flatten as much as possible
Allow to set in fridge for 2 hours and cut into desired shapes.