Prepare a 9 to 10 inch loose-bottomed non-stick tart tin, by base-lining with baking paper.
Coarse-crush the biscuits by placing in a plastic food bag and bash with a rolling pin.
Melt the coconut oil in a medium-sized bowl in the microwave or in a saucepan over a very gentle heat.
Add the crushed biscuits and chopped nuts to the pan and stir until evenly coated with the oil.
Pour the biscuit mix into the base of the tin and spread across the bottom, gently pushing up the sides of the tin with the back of a spoon until there is an even layer which forms a tart-case.
Place in the fridge for about an hour to chill and set.
In a large bowl, beat the double (heavy) cream with a whisk until it holds its shape in peaks.
Add the condensed milk, lemon zest and lemon juice and a small drop of lemon food colour (if using). Beat until thick.
Pour into the chilled tart case and place in the fridge for about 3 hours to set.
When set, carefully remove the tart from the baking tin and place on a serving plate. If the sides have stuck, gently apply pressure to the outside of the tin by squeezing a little and the stuck bits should release. Carefully remove the baking paper from the base before placing on the plate.
Dark Chocolate Ganache
Place the chopped chocolate in a medium-sized bowl and in a small saucepan, gently heat the cream until it just reaches simmer-point.
Pour the cream over the chocolate and allow to sit for 15 seconds, before gently stirring to melt the chocolate and combine. You should end up with a smooth ganache. If there are any remaining chocolate chunks which don't melt, microwave on medium setting for 30 seconds and re-stir.
Allow to cool completely at room temperature, stirring frequently as it cools and thickens.
Keep a close eye to avoid the ganache becoming too set.
Once the ganache has reached piping consistency, use a piping bag and with your chosen tip, pipe around the edge of the tart.
Place the water and sugar in a medium saucepan and stir over a low heat until the sugar has dissolved.
Now bring to a boil and add the sliced lemon.
Coat the lemon with the sugar liquid and continue to boil, turning frequently using tongs or a fork, cooking for about 10 minutes (until the lemons become more translucent).
Using Tongs or a fork , transfer the lemon pieces to non-stick baking paper to cool completely (separated) before using them to decorate the tart.
Sprinkle the tart with lemon sherbet and grated chocolate (optional).
Store in the fridge until ready to serve.
* Note: nutritional information is an estimate & may vary according to portion size/ingredient variants.For suggested substitutions to make dairy free or vegan, see main post.If unable to find chocolate biscuits which contain stem ginger, use ordinary chocolate digestive-type biscuits and add a little chopped stem ginger to the base mix.