Wet the pot with water.
Add the sugar, flour and starch and mix to combine.
Pour on the milk and cook over medium heat while continuously mixing.
Remove from heat when the mixture thickens and bubbles start to pop up.
Immediately add a tablespoon of butter, a lemon's zest and a teaspoon of vanilla extract.
Blitz the biscuits in a food processor until crumbly. Mix the crumbled with a tablespoon or two of butter. Transfer into a 25x25cm pyrex dish and press down to make firm and flat.
Pour the pudding on top. Let cool in the fridge. The pudding will get firmer when chilled.
Sprinkle with ground cinnamon before serving.