Grease a 26 cm spring form with little butter and dust with little flour. Mix flour and baking powder in a bowl.

In a mixing bowl beat the eggs with sugar and vanilla on high speed until double in size. Add the melted butter and continue beating for 2 minutes. Reduce speed to low and gradually spoon in the flour and continue beating on high speed for 1 minute until batter is creamy. Pour in the batter into the prepared pan.

Arrange the rhubarb pieces in one layer by pressing them half way into the batter. Sprinkle with one tablespoon sugar and bake at 175°C / 350°F for about 40 minutes or depending on your oven. Do the toothpick test!

If covering with meringue, bake the cake first, and then evenly cover with the prepared egg whites and continue baking for 20 minutes, lowering oven temperature to 160°C to keep meringue from turning very brown.

To make the meringue: In a clean mixing bowl and with an electric hand mixer beat egg whites with a pinch of salt on very high speed until the mixture is fluffy, then gradually and slowly add the sugar in while still beating until very stiff. Spread immediately over the baked cake and follow step 4. Don’t prepare the whites beforehand!