Preheat oven to 400F. Line an 11 inch tart pan (one with a loose bottom) with baking paper by cutting out a circle that fills the base.

Mix together crushed biscuits/crackers and butter, then press into lined tart pan to create the crust. Put this into the fridge to chill.

In a food processor, place the 1/2 cup sugar. Pulse on it's own for 1 minute to create a finer texture of sugar. (If you have caster sugar on hand, use that and you can skip this step). Add the softened butter and mix.

Add the beaten eggs and pulse in the food processor until combined. Add the almond flour and extract and pulse for 1 more minute.

Line chilled crust with thinly sliced apples, then spoon the frangipane filling over the top and spread until smooth. Sprinkle evenly with flaked almonds.

Bake for 25-30 minutes at 400F or until top is browning and set. Be aware some juices may escape from the tart pan so consider putting a baking sheet on the level below. 

Allow the tart to cool for at least 10 minutes before removing from the tart pan. To remove place the tart pan on a large can of beans or similar from your pantry and carefully pull down the edges. The crust can be crumbly. Serve warm with whipped cream if desired (I also like it chilled, without any topping).