1.Preheat oven to 180°C (180°C fan-forced). Grease two oven trays, line with baking paper.
2.Beat butter, sugar, egg yolk and combined coffee and water in small bowl with electric mixer until smooth. Transfer mixture to large bowl, stir in sifted flour and cocoa, in two batches. Knead dough on floured surface until smooth.
3.Roll level tablespoons of mixture into balls, place 5cm apart on trays, flatten slightly. Press 1 chocolate Melt into centre of each cookie; bake about 12 minutes. Cool cookies on trays.