Slice the rhubarb into large chunks and place into a deep baking tray. Sprinkle the 50 grams of sugar over and cover with tinfoil.
Bake at 180°c (360°f) for 10 minutes until barely softened.
Once cooked, remove from oven and remove tin foil. Allow to cool slightly.
In a large mixing bowl, add the eggs, ground almonds, sugar, baking powder and almond essence. Whisk together until a smooth batter has been formed.
Add half the rhubarb to the cake batter and fold in with a rubber spatula.
Pour into a greased and lined baking tin.
Sprinkle the rest of the rhubarb over the batter, along with the flaked almonds.
Bake for 40 minutes at 170°c (340°f) or 160°c (320°c) if fan assisted or until a skewer inserted into the middle comes out clean.