If you are using silicone mold, it's best to start with the lime mousse the day before so it can be frozen overnight. Everyone else can make the mousse last and spread it lightly over the tart.

For the lime mousse:
Melt the white chocolate. Beat the egg white until stiff (reserve the yolk for the crust). Beat the sour cream with lime juice, lime zest, vanilla, and locust bean gum, then stir in the melted chocolate. Fold in the egg white. Pour the mousse into the mold, shaking well to avoid air bubbles. Smooth the surface and freeze overnight. Alternatively, spread the mousse directly over the finished tart.

For the almond crust:
Grease the tart pan. Mix flour, ground almonds, salt, and powdered sugar. Blend the soft butter with almond butter and the egg yolk (the egg white will be used for the mousse), then add lime juice and vanilla. Knead in the flour mixture. Roll the dough thinly between two sheets of baking paper (about 3 mm thick) and place it in the pan.
Prick the dough a few times with a fork and chill it in the fridge. Preheat the oven to 180°C. When the oven is hot, cover the tart with baking paper and fill it with dried beans. Blind bake for 10-12 minutes. Remove the baking paper and beans, then bake for another 3-4 minutes until golden. Remove from the oven and let cool.

For the rhubarb curd:
Bring the rhubarb and beetroot juice to a boil and simmer for about 10-15 minutes until the rhubarb has broken down. Strain through a fine sieve, catching the juice (the solid part tastes wonderful with some yogurt and maple syrup). Measure 140 g of juice and mix with lime juice. Mix sugar and cornstarch until lump-free. Put the eggs in a small, heatproof bowl and whisk. Bring the juice with the sugar and cornstarch mixture and vanilla to a boil and simmer for about 1 minute. Pour quickly into the beaten eggs, whisking vigorously to prevent curdling. Return the mixture to the saucepan and thicken over medium heat, stirring until a creamy consistency forms. This takes about 5-8 minutes.
Pour the curd onto the almond crust, but not all the way to the edge, as the compote will also be added – some curd may be left over.

For the apple compote:
Peel and finely grate the ginger. Wash, core, and finely dice the Granny Smith apple. Cook 120 g of apple with ginger, lime juice, and sugar in a small saucepan for about 5-7 minutes. Stir in the cornstarch and cook for another 2 minutes. Remove from heat and fold in the remaining apple cubes. 
Spread the compote over the curd.

Final assembly:
Either press the lime mousse out of the mold and place it on the tart or spread it lightly over the tart. The tart can be served immediately but is also delicious the next day after resting a bit. Store in the refrigerator! 

Enjoy!