Preheat the oven to 180C / 160C Fan / Gas Mark 4. Line a 20cm square tin with non-stick parchment paper.
First, make the cookie base. In a large bowl, beat together the butter and the sugar until light and fluffy. Beat in the egg and the Vanilla.
Stir through the flour, cornflour, bicarbonate of soda, salt and chocolate chips.
Pour the mix into the prepared tin and press into an even layer.
Bake for 20-25 minutes or until the cookie dough is still a little wet to the touch. Allow to cool fully.
For the Caramel layer, put the butter, sugar, golden syrup and condensed milk into a large pot over a medium heat. Stir the mix continuously, until the sugar dissolves.
Turn up the heat and boil for 5-7 minutes, stirring all the time to ensure the mixture doesn't burn.
Once the caramel is golden in colour and has thickened to a soft fudge consistency, remove from the heat.
Stir in the salt, then pour the caramel over the cookie base and leave to cool for 1 hour or until just set.
In two separate bowls, melt the chocolate according to package instructions.
Spread the melted milk chocolate over the caramel layer and add some dollops of melted white chocolate on top. Using a skewer or the back of a spoon, swirl the chocolate to give a marble effect.
Scatter a mix of chocolate eggs and Mini eggs on top to decorate.
Once decorated, allow the chocolate to set in the fridge for 5 minutes. Cut into squares of your desired size and enjoy. These will keep for up to 1 week in an airtight tin.