1.To make cookie dough, beat butter, vanilla extract, sugar and egg in a large bowl with electric mixer until creamy. Stir in sifted flour, in two batches.
2.Knead dough on floured surface until smooth. Cover, refrigerate 1 hour.
3.Preheat oven to 160°C (140°C fan forced). Line trays with baking paper.
4.Using rolling pin, gently tap wrapped lollies to crush slightly. Unwrap lollies, separate by suggested colours into three small bowls.
5.Working with half the dough at a time, roll dough between sheets of baking paper until 4mm (⅛-inch) thick. Cut out three 12cm (4¾-inch) square bases. Place bases on tray, bake about 10 minutes. Cool on tray.
6.Cut out 15 x 10cm (4-inch) square walls from remaining dough. Place walls on trays.
7.Using heart-shaped cutter, cut out the centre of each wall to make windows, bake walls 10 minutes. Remove trays from oven, fill windows with crushed lollies (each colour will need to fill five windows). Bake about 2 minutes or until lollies have melted. Cool on trays.
8.To make royal icing, sift icing sugar through a fine sieve. Lightly beat the egg white into a small bowl until mixture is just broken up (do not whip into peaks). Beat in the icing sugar 1 tablespoon at a time, until it reaches desired consistency. Using a wooden spoon mix in the lemon juice.
9.Divide royal icing among three bowls, tint one yellow, one pale pink and one darker pink.
10.Spoon one portion icing into piping bag. Assemble and join walls to base using icing. Leave to set at room temperature. Repeat with remaining icings, bases and walls.
11.Place tea light in each box. Light to sing happy birthday. Place remaining wall on top, slightly angled to allow heat to escape.
Equipment 2 large oven trays 6.5cm (2¾-inch) heart-shaped cutter small piping bag fitted with small plain tube Sprinkling lollies into heart shapes Joining boxes with royal icing The tea lights should only be left alight for a short time or the heat will melt the windows.