Heat oven to 180˚C (350˚F). Take a baking tin of around 20 by 30 cm (8 by 12 inch) and line it with baking paper. Now add the (cold!) butter with sugar and almond flour to a food processor. Pulse until you have the texture of breadcrumbs. Take half of the mix out and set aside in a separate bowl.
Now to the rest of the mix in the food processor you add an additional 140 grams of flour (5oz) and turn till it forms a dough.Add this to the prepared baking tin and press it firmly into the tin with the back of a spoon or with the back of a glass.Place into the oven and bake for 15-20 minutes until golden brown. Take out and let it cool for 10 minutes while you work on the filling.
To finish making your filling you place the half of the mixture you took out earlier and put it back into the food processor. Add the rest of the butter and sugar and keep a few tablespoons of the crumble for the topping.
Add the eggs one by one with 25 grams of flour, cinnamon and baking powder and turn to a soft batter. Spread this over the cooled base.
Press the plums into the filling and sprinkle with a little granulated sugar and cinnamon. Bake for 20 minutes, take it out and then sprinkle with the remaining crumble mix and the flaked almonds. Bake for another 20 minutes or until golden brown.
Let it cool in the tin before slicing. Serve with whipped cream or vanilla ice cream!