Prepare the base:
Line a square or rectangular dish (about 20×20 cm) with a single layer of Tennis biscuits.
Set aside.
Make the creamy filling:
In a mixing bowl, combine the Cremora and boiling water.
Whisk until the Cremora dissolves completely and the mixture is smooth.
Allow it to cool slightly (about 5 minutes).
Add the condensed milk, instant vanilla pudding powder, and vanilla essence.
Beat with an electric mixer for about 2–3 minutes, until thick and creamy.
Assemble the slice:
Pour half of the filling over the first layer of biscuits and spread evenly.
Add another layer of Tennis biscuits on top.
Spread the remaining filling evenly over the second biscuit layer.
Finish with a final layer of Tennis biscuits on top (optional, for a traditional “slice” look).
Chill to set:
Refrigerate for at least 4 hours, or until firm and sliceable (overnight is best).
Serve:
Cut into neat squares or rectangles.
Dust lightly with icing sugar or drizzle with melted white chocolate if you’d like to dress it up.