Line a 20 cm (8 inches) square cake tin with parchment paper, extending it over two opposite sides for easy removal.
Crush or chop the oreo cookies into small pieces.
Place the sweetened condensed milk, chocolate, butter, and salt in a small saucepan and heat over low/medium heat until the chocolate has melted but do not boil. Remove from the heat.
Add the crushed oreo cookies and gently mix in.
Pour the mixture into the prepared pan and smooth the surface. Tap the cake tin on the bench several times to remove any air bubbles.
Add the topping. Twist 2 -3 oreo cookies to separate them into half, break them into pieces and gently press cookie pieces on top of the fudge.
Cool to room temperature, then place in the fridge for about 1 hour or until set.
Remove from the pan, cut into 36 squares, and store in an air-tight container at room temperature or in the fridge.