Heat oven to 180C/160C fan/gas 4 and line a few baking trays with baking parchment. Melt the butter, condensed milk and syrup in a large saucepan.
Very roughly crush the cornflakes in a bowl with your hands, then stir in the oats, flour, custard powder and bicarb, and mix really well.
Once everything in the pan has melted, take it off the heat and stir in the dry ingredients. Roughly scoop heaped tablespoonfuls of the mixture onto the baking sheets. Crumble over a few more cornflakes, then squash to flatten a bit with your hands.
Bake for 12-15 mins until golden. Cool on a wire rack.
