Preheat the oven to 150C/130C Fan/Gas 2 and line two baking trays with greaseproof paper.
Combine the ground almonds and icing sugar in a large bowl and whisk using a balloon whisk. Stir in the rosewater with a rubber spatula, then gradually add the water to make a smooth, stiff paste. Lightly dust a clean work surface with icing sugar, turn the dough out and roll out the mixture into a sheet just under 1cm/½in thick.
Use a 20cm/8in fluted tart tin to cut out a large circle from the dough. Transfer to a prepared baking tray and bake for 20 minutes, or until pale golden and firm.
Gather up the scraps of paste, re-roll, then cut out decorative shapes such as hearts, flowers and stars. Transfer to the second baking tray and bake for 15 minutes. Leave the cooked disc and shapes to cool completely.
Mix together the icing sugar, rosewater and enough water to make a pourable icing in a bowl. Place the disc on a wire cooling rack set over a baking tray, then pour the icing over to completely cover the disc, including the sides. Set a little of the icing aside. Gently shake the wire rack to even the surface then set aside for an hour to set.
Spray the decorative shapes with the gold and red sprays and then stick them to the surface of the disc with dots of the excess icing. Leave to set for 30 minutes.