2Combine base ingredients (melted butter and crushed Oreos) in a bowl, stir until butter coats the crumbs. Pour into prepared tin and press down firmly. Refrigerate.
3In a saucepan, melt caramel ingredients (condensed milk, butter, sugar, and golden syrup) over medium-low heat. Once melted, turn heat to medium-high and stir for 8-10 minutes until the caramel thickens.
4Pour the caramel over the base and refrigerate for at least 2 hours.
5Once set, pour melted Nutella over the caramel, then pour melted white chocolate over Nutella. Swirl with a butter knife and sprinkle with crushed Oreos. Refrigerate for ~2 hours.