1.Preheat oven to 180°C/350°F. Grease oven trays; line with baking paper.
2.Beat butter, sugar and syrup in a small bowl with an electric mixer until combined. Beat in eggs, one at a time. Transfer to a medium bowl; stir in sifted flour, and coconut and oats.
3.Roll rounded teaspoons of mixture into balls; place 5cm (2-inches) apart on trays, flatten with the palm of your hand until 4cm (1½-inches) round. Using a flour-dusted fork, mark cookies. Bake 12 minutes or when a biscuit is gently pushed it moves without breaking. Cool on trays.
4.Meanwhile, make milk chocolate ganache. Stir chocolate and butter in a small heatproof bowl over a small saucepan of simmering water until smooth (don’t let water touch base of bowl); cool ganache until spreadable.
5.Sandwich two biscuits with 2 teaspoons of ganache; refrigerate until firm, if required.
Plain biscuits will keep in an airtight container for up to 1 week. Sandwiched biscuits will keep, refrigerated, in an airtight container for up to 3 days. Be sure to use quick-cooking oats, which are rolled thinner than traditional rolled oats, or the texture of your biscuits will not be crunchy.