Katukivikakku Finnish Gobble Stone Cake

Melt the butter and add a pinch of salt if using unsalted butter and preheat the oven 375F (175C) Cut rhubarb in a 1/4" (1cm) long pieces. Whip the eggs and sugar until nearly white. Add most of the flower and blend it in. Mix rest of the flower with baking powder. Add the melted butter and mix it in. Cover a 18" x 12" oven roasting pan with baking parchment. Spread rhubarb over the top and sprinkle with some cinnamon and sugar. Bake 10-20 minutes. The same recipe can be used for making an apple cake. Use in that case baking apples like Gravensteiner. Also European blue berries work well (the US kind are too bland for this). Also a mix half sour and half sweet cherries should work well.