Mix the flour, sugar and vanilla seeds in a separate saucepan until smooth, then whisk in the warm milk, a little at a time, until smooth. Place the pan onto the heat and cook over a gentle heat for 2-3 minutes, stirring continuously.
Whisk in the Amaretto liqueur and continue to whisk until the mixture thickens.
Remove the pan from the heat and stir in the chocolate and butter.
To serve, spoon the mixture into serving glasses and sprinkle over the crushed amaretti biscuits.