Place the butter in a bowl, whisk in the sugar and salt. Add the eggs one at a time and continue to beat until the mixture becomes lighter in colour. Add the lemon zest and juice, mix. Combine the flour and baking powder, stir into the mixture. Transfer the cake batter to the prepared tin. Place the plum halves vertically into the batter and sprinkle with the flaked almonds.
Approx. 60 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, leave to cool in the tin.
Beat the cream with the sugar and cinnamon until stiff, serve with the cake.