Pulse flour, butter, salt, and icing sugar in a food processor into fine breadcrumbs.
Add beaten egg and cordial until dough forms, then knead lightly and chill for 30 minutes.
Preheat oven to 150°C and grease a 12-hole tart tin.
Roll pastry, cut 7.5cm circles, place in tin, prick with a fork, and bake for 10-12 minutes.
Boil honeycomb sugar, honey, water, and glucose to 160°C, then whisk in bicarbonate of soda.
Pour honeycomb onto a lined tray to cool, then break into shards.
Whisk sugar, egg, yolk, and cornflour in a bowl while heating milk and cream to a simmer.
Whisk hot liquids into egg mixture, then heat until thickened and leave to cool.
Stir elderflower cordial into the cooled cream.
Pipe cream into cases, top with honeycomb, and garnish with a flower.