Place butter in a small sauce pan and heat on low until melted. Set aside.
Wash and pat dry your kumquats. Slice them in halves and remove the seeds. Then, gently blend them on a purée mode to keep some texture.
In your mixing bowl, whisk the kumquat purée with the confectioners sugar together. Then, taste if the sweetness is to your liking (Depending on how ripe the fruits are, you may need to sweeten accordingly. Add a tablespoon of confectioners sugar at a time). Whisk in the eggs, Greek yogurt and the cooled melted butter. Fold the all-purpose flour, baking powder and almond flour.
Pour your batter into the Flexipan®. Flatten evenly with your spatula.
BAKE!
Bake for 40 minutes at 350F/180C. (Every oven heats differently, monitor your cake from 35min). It is ready when the toothpick inserted comes out clean.
Once your kumquat cake is out of the oven, let it cool down for about 10min. Then, Unmold and pour the rest of the sirop over. Serve and enjoy! Bon appétit!