Preheat oven to 190 C / Gas 5. Grease a 25cm loose-bottomed tart tin or line with baking parchment.
In a blender or food processor, mix together all the ingredients for the pastry until it resembles breadcrumbs. Turn out on a worktop and form quickly to a ball. Dust a large piece of cling film with flour and place pastry on top. Place a second piece of cling film on top and roll out to fit a 25cm springform tin.
Press the pastry onto the bottom and the sides of the prepared tin and prick with a fork. Cover with a sheet of baking parchment.
Bake blind for about 15 minutes in the preheated oven, until firm but not hard. Let the pastry cool, then carefully remove the baking parchment and bake for another 5 minutes.
Peel apples, core and thinly slice. Evenly layer the apple slices over the pre-baked pastry case.
In a bowl whisk together creme fraiche, vanilla extract and eggs and pour over the apples.
Bake for about 30 minutes, until cake is set and golden brown on top. The filling should still be a little wobbly. It gets firmer when the tart cools down. It is best to set the tart tin on a baking tin, to avoid spills in the oven.
Press apricot jam through a sieve. Combine with some water in a saucepan and heat, until runny. Brush the jam over the cake. Sprinkle with cinnamon and sugar and place the cake for 1 to 2 minutes under the grill until golden brown on top.