Preheat the oven to 180C and prepare a baking tray.
In a bowl, combine the butter, caster sugar and ground almonds, then add the egg. add a little of lemon juice if desired. Keep aside until needed.
Slice the croissants in half lengthways.
Spread a layer of almond cream over each pastry base and sprinkle a few flakes almonds.
Close the croissant and drizzle the leftover almond cream on top of the croissant.
Sprinkle with the rest of the flaked almond and place on the baking tray.
Bake in the oven for 10-15 minutes or until golden brown.
Remove from the oven and serve warm with a tasty cup of tea!