Blitz the biscuits into crumbs using a food processor, or you can put them in a bowl or freezer bag and bash them up with the end of a rolling pin
Place the biscuit crumbs into a bowl. Add the melted butter and mix it in
Press the biscuit mixture into the base and sides of a 9" loose bottomed tart tin
Put the biscuit base in the fridge while you make the filling
Put the icing sugar into a large saucepan (the mixture will more than double in size when it boils so use one with high sides), then add the cream slowly, whisking as your pour. Mix the icing sugar and cream together until smooth
Zest the lime into the cream mixture
Heat the cream mixture to a boil, stirring it constantly all the time. When it boils, let it boil for 2 minutes, again stirring it constantly while it boils
Take off the heat and stir in the passion fruit puree and vanilla extract
If you want to remove the lime zest, strain the mixture through a fine sieve into a jug. If not, pour the mixture straight into a jug
With the biscuit base still in the fridge, pour the filling into it. This will save any spillages trying to carry it to the fridge as you want the filling to be right to the top
Leave in the fridge for at least 4 hours, or ideally overnight, to set
For decoration, whip up the double cream with the icing sugar
Remove the tart from the tin and pipe the whipped cream around the edges. Then garnich with some fresh passion fruit
Store the tart in the fridge and eat within 3 days