For the pastry, mix the flour, ginger, lime zest, icing sugar and almonds in a large bowl. Add the butter and rub in with your fingers until you have a consistency like fine breadcrumbs.
Add 1/3 of the beaten egg, and mix by hand just until fully combined. Pull it together into a ball - if it seems too terribly crumbly, add a drop or two more of the egg just until the ball holds together. (You don't want it to be too wet, as it could shrink out of shape when baking.) Flatten it into a thick disc and wrap in clingfilm. Chill in the fridge for at least 1 hour, or overnight.
Preheat oven to 190 C / 170 C Fan / Gas 5. Grease your tin and line with parchment. The tin should be 23-25cm in diameter and 5cm in depth.
Lightly flour a work surface and a rolling pin. Roll out the chilled dough approximately the thickness of a pound coin, to fit the tin so the pastry goes all the way up the sides. If you're using a fluted tin, ensure the pastry is pushed into each nook and cranny. Lightly prick it all over with a fork. Line the pastry case with baking paper, and pour in baking beads or dried beans.
Blind-bake in the preheated oven for around 10 minutes, then remove from the oven. Tip out the beads or beans into a small bowl and discard the lining paper. Return the tin to the oven, and bake for around 15 more minutes until the pastry is evenly browned.
Remove the tin from the oven, and brush the pastry all over with the rest of the beaten egg to seal it for the filling.
For the filling, grate one of the lemons with a citrus grater to get large-ish strips of lemon zest; set aside. Zest the other two lemons normally to get finely grated zest. Finally, halve and juice all three lemons.
After the pastry has baked, turn the oven off and spread the largely grated lemon zest on an oven-safe plate, breaking up any clumps. Place in the oven and leave to dry out - door ajar - as the oven cools.
Combine the finely grated lemon zest, lemon juice, lime juice, double cream, mascarpone, soured cream, egg yolks and 130g sugar in a bowl over a pan of gently simmering water on the hob (ensure the bottom of the bowl doesn't touch the water). Whisk manually, quite briskly and frequently, for 15 to 20 minutes until hot and thickened slightly.
Cover the gelatine leaves with cold water in a small bowl. Leave for 5 minutes or until softened, then squeeze all extra liquid out and add to the cream mixture, still on the heat, whisking briskly until dissolved. Remove the bowl from the heat and allow to cool for 10 minutes, whisking regularly.
Beat the egg whites to stiff peaks, starting at low speed and gradually increasing to high speed as the colour and texture change.
Gently fold the egg whites into the cream mixture until no large lumps or streaks of white remain. Pour into the baked pastry case and drop from an inch height - gently! - to remove any air bubbles. Chill in the fridge for at least 2 hours (you can put it into the freezer for 30 minutes for a quick-chill).
Mix 2 pinches of caster sugar with the dried lemon zest, ensuring all strands are coated, and sprinkle over the cheesecake to garnish. You can also dust with icing sugar if you like before serving.
All large eggs should be between 60g and 68g when weighed in the shell.