In a bowl, add softened butter and icing sugar. Whisk it well till light and fluffy and all the sugar is dissolved.
Then add flour, custard powder and milk. Mix it well to form a soft pipeable dough. Transfer the dough into a piping bag fitted with an open star nozzle.
Pipe the cookies on a plate lined with parchment paper and freeze for 10-15 minutes.
For baking, set a pan on medium-low heat and spread a layer of salt in it. Place a small stand in it and cover it. Let it preheat for 5-10 minutes.
Once preheated, carefully place the cookie plate over the stand and cover again. Let it cook for 12-15 minutes or until the edges become golden brown.
Recipe by Bake with Shivesh at https://bakewithshivesh.com/custard-cookies/