Cream butter and sugar until fluffy. Gradually stir in egg whites, lime juice and zest. Finally, mix in the flour.
Fill the mixture into a piping bag and pipe small sticks with a smooth nozzle onto a prepared baking tray.
Bake in the preheated oven at 165 to 175 °C for about 10 minutes until light brown. When cool, spread half of the cookies with lime cream on one side and place the other half on top.
Base cream:Boil milk with sugar. Reserve a little milk and mix it with the custard powder. Stir this mixture into the boiling milk and cook to pudding.
Pour hot pudding into a mixing bowl and cool slightly while stirring with a whisk.
Add the chopped butter pieces or coconut oil to the still not quite cold pudding mixture and whip until fluffy. Then add the desired lime juice.