01 - Crush biscuits into fine crumbs using a food processor or by placing in a sealed bag and rolling with a rolling pin. Set aside.
02 - In a mixing bowl, whip cold heavy cream with powdered sugar and vanilla extract until stiff peaks form. Transfer to refrigerator until assembly.
03 - Combine granulated sugar and water in a saucepan. Heat gently, stirring until dissolved, then simmer for 3 to 4 minutes to form a light syrup.
04 - Lightly whisk egg yolks in a separate bowl. Gradually pour hot syrup into yolks while whisking constantly.
05 - Transfer yolk mixture back to saucepan and cook over very low heat, stirring continuously, until slightly thickened without boiling. Remove from heat and cool completely.
06 - Layer half of the biscuit crumbs at the bottom of serving dish or individual glasses.
07 - Spoon half the whipped cream over biscuit layer and spread evenly.
08 - Add remaining biscuit crumbs, followed by the rest of the whipped cream.
09 - Pour the cooled egg yolk custard over the top as the final layer.
10 - Refrigerate for at least 2 hours before serving to set the layers.