Preheat oven to 180°C (350°F) /160°C (320°F) fan-forced. Grease and line a 20 x 20cm (base measurement) square slice tin or a 27.3 x 17.5cm (base measurement) rectangle slice tin with baking paper hanging over the edges.
Place flour, sugar, butter and coconut in a bowl and mix well. Press the mixture thinly into the bottom of the prepared tin. Bake in the pre-heated oven for 15 minutes until golden. Remove from oven and cool for 15-20 minutes.
Place the condensed milk, butter and golden syrup in a saucepan over very low heat. Stir constantly to avoid sticking and cook for about 5-7 minutes until the caramel has thickened and is smooth. If you feel that the butter rises to the top, remove from heat and continue mixing until smooth and creamy.
Pour caramel mixture onto the baked cooled cookie layer. Bake in the oven for 18 to 25 minutes until the caramel is golden and starts browning in spots (burnt butter effect!). (I start watching the top from the 15-minute mark, if it is starting to brown very quickly, I take the slice out of the oven)
Remove from the oven when you see it starting to brown on top. Cool for a couple of hours until firm and then slice and serve. Alternatively, wait 15 minutes until cooled slightly before slicing.