Mix the custard powder, sugar and vanilla in a pot. Gradually add cold milk and stir until well blended. Bring to a boil over medium heat. Continue cooking over medium-low heat, stirring constantly until thickens (about 10-11 minutes). Remove from the heat and let the custard cool down to room temperature.
Meanwhile, melt the butter in a pan over low heat. Add the crushed biscuits, mix well and fry for 2-3 minutes.
Squash a layer of crumbed biscuits (2-3 teaspoons) into the bottom of each dessert dish. Place them in the refrigerator for 15 minutes.
Then pour custard mixture over the crumbed biscuits.
Refrigerate for 4-5 hours and serve.