First line the container with two pieces of cling film/plastic wrap so they are laid across one another and large enough to overhang the edges of the container on all sides. Press well into the corners of the container.
For the base
In a medium bowl, combine the chocolate crumbs and sugar. Stir in the butter to coat the crumbs.
Now spread evenly in the container, using a flat bottomed glass or measuring cup, pressing well into the corners.
Freeze while making the filling.
For the filling
Remove the ice cream or frozen yogurt from the freezer to soften a little while preparing the strawberries.
Slice the strawberries and put in a small bowl. Toss with the sugar and leave for 10 minutes, tossing occasionally.
Purée the strawberries until smooth.
Scoop the ice cream or yogurt into a large bowl. It should be soft but not completely thawed. Then pour over the strawberry purée. Stir until well blended.
Spoon evenly over the chocolate base and freeze until firm, about 4 hours.
For the topping
Start preparing the toasted almonds and chocolate sauce about one hour before serving so they have time to cool.
Tip the almonds into a small frying pan/skillet and toast over a medium to low heat until golden, tossing frequently. They will take about 5–10 minutes but keep an eye on them as they burn quickly. (They produce a nutty smell when ready.) Put to one side.
Break the chocolate into small pieces and add half to a glass bowl.
Melt the chocolate by sitting the bowl over a pan of just simmering water. (The bowl should not touch the water.)
Remove the bowl from the heat and add the remaining chocolate pieces.
Stir until the chocolate has melted and there is a smooth sauce. Leave to cool.
Top each square just before serving.
Holding the edges of the baking parchment, remove the frozen sundae to a cutting board. Now using a serrated knife, cut into six even pieces. Leave for 10 minutes to soften a little.
Slice the remaining strawberries and decorate the top of the squares.
Then drizzle over the chocolate and sprinkle with the toasted almonds.
Once the base and filling has frozen, it can be cut into portions and then the portions returned to the freezer until needed. The topping is added just before serving and is better not frozen.
This is a great recipe to make and keep in the freezer. The quantities can be doubled to be able to freeze more portions; but use a 24 cm (9½ in) square container.