Preheat oven to 180°C fan-forced. Grease and line a 20x30cm slice tin.

Whisk eggs and sugar on high until pale, thick and tripled in volume (about 8 minutes). Add vanilla.

Sift flour over the eggs in thirds, folding gently with a spatula. Combine melted butter and warm milk, fold in last.

Pour into tin. Bake 22-25 minutes until sponge springs back. Cool in tin 10 min, turn out to cool fully. Wrap and chill overnight.

Trim sponge edges. Cut into 16 squares. Put cubes on a tray in the freezer for 20 minutes.

Sift icing sugar and cocoa into a heatproof bowl. Stir in butter and boiling water until smooth. Sit bowl over simmering water to keep liquid.

Spread coconut in a wide shallow tray. Using two forks, dip each frozen cube in icing, letting excess drip off, then roll in coconut. Place on a wire rack to set.

Leave to set for 30 min before serving. Keeps in an airtight container for 5 days.