Preheat oven to 150ºC and turn on ice cream machine to chill.
For the custard apple ice cream, bring milk to the boil in a small saucepan. Whisk egg yolks and sugar together by hand, then pour boiling milk onto the egg yolk mixture while whisking. Pour into a stainless steel bowl and cook while whisking over a pot of simmering water for about 10 minutes or until it is thickened. Whisk sabayon until cool over ice. Set aside. Scoop the flesh of one custard apple at a time into a double muslin lined chinois sitting over a measuring jug. Gather the muslin cloth at the top and squeeze tightly to obtain a clear juice. When you have 150ml, whisk it into the sabayon with the cream. Place the mixture into an ice cream machine and churn for about 40 minutes. Place in the freezer until set.
For the vanilla custard base, heat cream and vanilla seeds together in a small saucepan until it just begins to boil, and then remove from the heat. Whisk by hand the eggs, egg yolks and sugar together in a stainless steel bowl until combined. While whisking the eggs, slowly pour on the hot vanilla cream. Mix well and remove the vanilla pods. Pour this mixture into 4 dariole moulds to a depth of 5 cm, place the dariole moulds into a small baking dish with boiling water around the dariole moulds up to halfway to form a water bath. Place the water bath into a 150ºC oven and cook the custard 25 minutes or until the custard is just set. If the centre is still runny place in the freezer until set then place in refrigerator until needed.
For the granita, combine sugar and water in a large saucepan; bring to the boil then lower heat. Add diced fruit and gently simmer for 10 minutes. Take off the heat and infuse at room temperature for 30 minutes. Pass the liquid through a muslin cloth and discard the solids. Pour the syrup into a lamington or slice tin to a depth of 5cm. Place in the freezer until solid. Scrape with a fork into crystals and then transfer to the freezer until required.
For the poached meringue, whisk the egg whites in an electric mixer until they form soft peaks and then slowly add the sugar bit by bit. Keep whisking until the meringue forms firm peaks and the sugar has dissolved. Spray hemisphere moulds lightly with canola oil spray. Spoon mixture into a piping bag fitted with a 1cm nozzle. Pipe mixture into moulds so it sits above the surface. Place the filled moulds into a large baking dish and pour boiling water into the baking dish to a depth of about 3cm. Bake at 150ºC for 15 minutes until just. Allow to cool for 2 minutes, then trim off tops so they are perfect hemispheres. Gently un-mould and place cut side up on a baking paper lined tray in the fridge until needed. Increase oven temperature to 180ºC.
For the guava puree, combine sugar, water and scraped vanilla bean in a saucepan and bring to the boil. Lower heat to a gentle simmer, add guava and simmer 10 minutes. Take off the heat, remove the vanilla pods, drain the flesh from the liquid, place the flesh in a blender and add just enough of the cooking liquid to process into a thick guava puree. Pass the puree through a fine sieve and set aside, covered, in the fridge until needed.
To make the maltose tuiles, stir maltose and sugar together in a small saucepan then bring to the boil until it reaches hard crack stage (until it caramelises). Take care to brush down the sides with a pastry brush dipped in water so it doesn't crystallise. Once golden add the flaked almonds and immediately pour the mixture onto a silicon mat, allow to cool completely. Process the cooled praline in the bowl of a hand blender to form a fine powder. Next sift a fine layer of the praline mixture through a drum sieve, over an acetate stencil with 11cm circles cut out of it onto a silicon mat on a baking sheet. Melt this mixture in a 180ºC oven for a few minutes until it forms a clear liquid paste. Cool tuiles slightly and peel off silicon sheet while still flexible. Store flat between sheets of baking paper until ready to use.
For the vanilla cream, whisk the cream and custard together to form soft peaks. Store in the fridge until ready to use.
For the guava fool, place the guava puree in a small bowl and fold through the vanilla cream gently to form a rippled effect. Do this just before you are ready to assemble the dessert.
To assemble, take 8 of the half hemisphere poached meringues. Using a teaspoon or half teaspoon measure remove a small scoop from the centre of each half hemisphere being careful not to break through the outer edge. Then place a teaspoon or half teaspoon measure scoop of custard apple ice cream in four of the hemispheres. Invert the other four hemispheres over the ice cream filled meringues to form a complete sphere. Use wet fingers to stick the two halves together. Place a tuile on top of each sphere and using a blow torch and an even motion, melt it over the sphere, patting it down if necessary. Dust spheres liberally with icing sugar. Next add a generous spoonful of the guava fool in the bottom of each serving glass. Top the fool with the guava granita. Use two teaspoons to place the snow egg on top of the granita and serve.