Step 1

Line an 18cm x 27cm slice tin with baking paper.

Step 2

In a food processor, crush biscuits into a fine crumb. Alternatively, place biscuits in a large zip-lock bag and bash with a rolling pin. Add butter and combine well. Press into the base of the prepared slice tin.

Step 3

Combine milk and vanilla in a small saucepan. Sprinkle over gelatine. Whisk over a gentle heat for 1-2 minutes until gelatine has dissolved, being sure not to let it boil. Remove from heat and allow to cool.

Step 4

In a large bowl, whisk together sour cream and sugar. Fold through whipped cream. Slowly add cooled milk mixture and whisk until well combined. Pour over biscuit base in slice tin. Refrigerate for at least 30 minutes until mousse has set.

Step 5

Slice into squares and serve.