Mix the flour, sugar and salt in a bowl, add the butter and rub by hand to form a crumbly mixture. Add the water, mix quickly to form a soft dough. Roll out the dough into a circle (approx. 5 mm thick) between two pieces of baking paper, chill for approx. 30 mins.
Sprinkle sugar over the base of the prepared cake tin, cover with the knobs of butter and plums.
Beat the eggs and sugar with the whisk on a hand mixer until light and fluffy. Stir in the crème fraîche, butter and ginger. Mix the flour, nuts and baking powder, fold into the mixture. Spread the cake batter over the plums, place the pastry base on top.
Approx. 1 hr. on a baking tray in the lower half of an oven preheated to 180°C. Remove and allow to cool slightly. Loosen the cake from the tin frame, turn out onto a plate, remove the tin base and baking paper, leave to cool. Serve with crème fraîche.