Whisk ghee and sugar until it is fluffy. Add the egg and yolks and continue to whisk until it is creamy. Add lemon zest, almond meal and the flour previously mixed with the baking powder.
Fill the cake batter into a small 18 cm/7 in springform pan (previously greased) and 6 muffin forms. Distribute the rhubarb pieces equally on cake and muffins.
Bake the cake for 35 to 45 minutes and the muffins for 20 to 25 minutes.
Meanwhile prepare the meringue. Beat the egg whites with the pinch of salt and apple cider vinegar until stiff. Then slowly add the sugar continuing to whisk.
Put the meringue mixture first on the hot muffins and spread some almond slices on the top. Put back in the oven and bake them for additional 15 minutes.
When the cake is ready, take it out and cover with the meringue, spread the rest of the almond slices on the top and put back in the oven for additional 15 minutes.
Let cool out the muffins and the cake and decorate with the colored icing sugar.
The cake is best when still a little warm when you serve it.
The meringue sometimes doesn't get really hard and crumble, that doesn't do anything to the taste. It is also great with a softer meringue on the top.
Don't ruin the cake by serving whipped cream with it. It just doesn't seem right!
The cake is great also the day after. I didn't put it in the fridge during the night but left it out, just covered with a piece of parchment paper. In the fridge it should be sealed in an air-tight container.