Preheat the oven to 170˚C (350˚F) and brush the baking tin with oil or butter. Place a bit of baking paper on the bottom of the tin.
Clean the rhubarb and slice into smaller pieces of about 1 cm each. Keep a few pretty pink ones for the top.
Whisk the butter and the sugar together until white and fluffy in a few minutes.
Mix the eggs in one by one.
Add the almond flour, orange zest, self raising flour, baking powder and the salt.
Divide half of the batter over the baking tin.
Divide half of the rhubarb on top and sprinkle with one tablespoon of the extra sugar.
Place the remaining batter on top and place the pretty rhubarb you kept on top.
Sprinkle with the remaining tablespoon of sugar and the almond slivers.
Bake the cake in the oven for about an hour. Make sure it is cooked when you insert a wooden stick. If it comes out clean, the cake is cooked. If not cooked yet but getting too brown? Cover with some foil and continue baking for another 15 minutes or until done.
Leave to cool and serve with whipped cream or ice cream.