Place the apples in the baking dish and mix with all the other ingredients up to and including the vanilla seeds.
Approx. 45 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, pass half of the apples through a food mill into a bowl, leave to cool, cover the baked apple slices and set aside.
Heat the cream and sugar in a pan. Pour half of the cream into the egg yolk, mix well, return to the pan, simmer over a medium heat, whisking constantly until the mixture thickens and turns creamy. Pour the mixture through a sieve and into the sour single cream in a stainless steel bowl, mix well. Stir in the apple sauce, leave to cool. Freeze for approx. 6 hrs., stirring vigorously with a whisk at least 4 times.
Bring the water and sugar to the boil in a pan, reduce to a syrupy consistency. Add the almond slivers, reduce over a medium heat, stirring constantly until the sugar is dry and sticks to the almonds, transfer to a sheet of baking paper, leave to cool.
Scoop the ice cream into balls, serve with the reserved baked apple slices and the sugar-roasted almonds.