Break the Marie biscuits into small pieces using your finger tips or using a rolling pin. Add the biscuits to a large mixing bowl and set aside.
In a small bowl, whisk the eggs and vanilla essence together and set aside.
And the butter to a small saucepan and bring to a medium heat, once melted, add powdered sugar, cocoa powder and salt. Mix until melted, approx. 2 minutes.
Remove from the heat, add the egg mixture and mix thoroughly until well. Note: the egg will cook in the residual heat but feel free to let the mixture cook for another minute or so, if you'd feel more comfortable.
Pour the fudge over the broken Marie biscuits and mix until fully combined.
Pour the mixture into a greased square or rectangular baking dish and press it down firmly with a spatula. Note: you can use whatever dish you like - make them as thick or and thin as you'd like. You can line the dish for easier removal, just loosen the edges before lifting.
Pop the fudge in the fridge for a minimum of 2 hours before cutting it.
Video
Notes
Feel free add any additional fillings or toppings. She's great as is but you can definitely use her as a baseline recipe for greater ones :) Just make sure there's enough fudge to bind it together.