Crush or blend biscuits to a bread crumb consistency.
Melt butter and stir through biscuit mixture to combine.
Pour biscuit mixture into a baking tray that's been greased and lined with baking paper. Spread evenly with the back of a spoon and then press down firmly with fingertips.
Place biscuit base in fridge to set.
Combine condensed milk, vanilla essence, chocolate (broken into pieces) and Kit Kat (broken into pieces and retaining two fingers for decorating) in a saucepan.
Place saucepan on medium heat and stir until melted and combined. This should take about 5 minutes.
Pour chocolate mixture over biscuit base.
Chop the remaining Kit Kat and sprinkle over top of slice.
Place in fridge and allow to set overnight.
Remove slice from the tin and then cut into squares.