Grease a 3.5cm deep, 16.5cm x 26cm (base) slab pan. Line with baking paper, allowing a 2cm overhang at both long ends.
Place condensed milk, sugar, butter, glucose and golden syrup in a large (14-cup capacity), heatproof, microwave-safe bowl. Microwave, uncovered, on MEDIUM-HIGH (70%) for 8 to 10 minutes, stirring with a balloon whisk every 2 minutes, or until mixture comes to the boil.
Microwave, uncovered, on MEDIUM-HIGH (70%) for a further 5 to 6 minutes, stirring every minute with a wooden spoon, or until thick and golden.
Place bowl on a board. Stand for 2 minutes or until bubbles subside. Add white chocolate. Stir until chocolate melts and mixture is smooth. Pour hot fudge mixture into prepared pan. Smooth surface. Stand at room temperature for 3 hours.
Refrigerate until firm. Lift out onto a board. Cut into squares.