1: Pre-heat the oven to 180C/160C Fan/Gas.
2: Put the butter, golden syrup, and sugar in a saucepan over medium heat, stirring until melted.
3: Off the heat, add chopped chocolate and vanilla extract; let it melt for a few minutes.
4: Chop the Lion bars into pieces and set aside.
5: Stir the melted chocolate mix until smooth, then whisk in eggs until thick and velvety.
6: Sift flour in batches, folding in until just combined.
7: Fold in rice crispies and Lion bar pieces.
8: Pour into a lined 20cm square baking tin and bake for 25-30 minutes until firm to the touch.
9: Cool completely in the tin; refrigerate for easier cutting.
