2.Process icing sugar, ground almonds, coconut and cinnamon until fine; sift through fine sieve into medium bowl, discard any large pieces.
3.Beat egg whites and caster sugar in small bowl with electric mixer until firm peaks form and sugar is dissolved. Fold in almond mixture, in two batches.
4.Spoon mixture into piping bag fitted with 1cm (½-inch) plain tube. Pipe 4cm (1½-inch) rounds, about 2.5cm (1-inch) apart, on trays. Tap trays on bench so macaroons spread slightly. Dust with sifted extra icing sugar. Stand about 30 minutes or until macarons are dry to touch.
5.Preheat oven to 150°C/300°F.
6.Make eggnog custard
7.Bake macarons about 20 minutes. Cool on trays.
8.Sandwich macarons with about 1 teaspoon of custard.
9.Combine cornflour, custard powder and sugar in small saucepan; gradually stir in milk. Stir over heat until mixture boils and thickens. Remove from heat; stir in butter, egg yolk and brandy.
10.Cover surface with plastic wrap; cool.
The custard can be made several days ahead; store in the fridge. Return custard to room temperature before using. Filled macaroons are best eaten the day they are made. Unfilled macaroons will keep in an airtight container, at room temperature, for up to 3 days or will freeze for 3 months.