1. To make the candied lemon slices, cut the lemons into thin rounds no more than 3mm thick, discarding the seeds and end pieces. Fill a large bowl with iced water and set aside. Bring a pan of water to the boil and add the lemon slices, then simmer for 1 minute. Remove with a tongs and quickly place in the iced water to allow them to cool down quickly.
2. Heat the sugar with the water and orange juice in a large sauté pan and simmer gently until the sugar dissolves, stirring occasionally. Reduce to the heat to medium-low and add the lemon slices in a single layer. Simmer gently for 45-60 minutes or until the rinds are slightly translucent, turning with a tongs every 15 minutes or so to ensure they cook evenly.
3. Using a tongs, transfer to a cooling rack and leave to cool completely for at least 1 hour or overnight is perfect to allow them to dry out completely.
4. Preheat the oven to 180C to make the cake. Grease and line a 20cm square tin. Cream the butter and sugar together with an electric mixer until light and fluffy. Whisking all the time, gradually add in the beaten egg, beating well between each addition and adding a teaspoon or two of flour each time. When all the beaten egg has been added, add the lemon rind, baking powder and vanilla and salt. Add any remaining flour, the ground pistachios and almonds and fold into the mixture. Spoon into the prepared baking tin. Bake for about 40 minutes or until a skewer inserted into the centre comes out clean. Once cool, remove the paper and trim down into 6 even-sized portions.
5. To make the glaze, put the sugar and lemon juice in a pan, stirring over a low heat until dissolved, then boil to reduce by half. Turn the cake portions upside down, then brush the bottom and sides with the glaze, then turn back over and brush the tops with the rest of the glaze.
6. To serve, put the pistachio & almond cake on plates and drizzle over a little more of the lemon drizzle, Add a candied lemon slice to each one. Decorate with the pistachios and add a scoop of ice cream to each one.
Vanilla Ice Cream
25g skimmed milk powder
50g glucose syrup
1 piece pared lemon peel
4 vanilla pods
100g caster sugar
4 egg yolks
1. Place the milk, skimmed milk powder, glucose syrup, lemon peel and vanilla pods into a pan. Place over a medium heat until it just comes to the boil. Take it off the heat and leave to cool.
2. Whisk the caster sugar and egg yolks together in a large bowl until thick and creamy, then whisk in the hot milk until evenly combined.
3. Pour the milk mixture back into a clean pan. The egg yolk will thicken the mixture but because there is not any cream present there is more of a risk that it might curdle so cook it over a low temperature, stirring constantly until the egg thickens enough to coat the back of a wooden spoon.
4. Pour the thickened custard into a bowl that is sitting over a bowl of ice. Then once cold, remove the lemon peel and vanilla pods.
5. Leave in the fridge for at least four hours and then pour into cryo bowl and add in liquid nitrogen, bit by bit until the ice cream is at the right consistency. Alternatively place in an ice cream maker and mix until you have achieved a smooth creamy texture. Keep frozen and use as required.