Preheat the oven to 180°C / 356°F.
Butter a large (12- to 13-cup) Bundt pan, dust the interior with flour, and tap out the excess.
Carefully separate the eggs into egg whites and yolks.
Beat the egg whites in a mixer at low speed, gradually increasing the speed to medium and then high until they form stiff, glossy peaks that stand upright when the beater is lifted from the bowl. Refrigerate the egg whites. Next, place softened butter in a mixing bowl, add the sugar, and beat on medium speed until the mixture is light and fluffy, pale yellow, and has visibly increased in volume, scraping down the sides of the bowl as needed.
Add the yolks and then, alternately, the yogurt with the flour and the vanilla.
Stop the mixer and slowly incorporate the meringue into the batter. Use a rubber spatula to slice down through the batter, lift it, and fold it over, ensuring you don’t overmix to preserve the air pockets in the meringue and maintain a light and fluffy texture.
Pour into the bundt pan and bake for about 50 minutes.
Insert a tester to ensure the cake is baked all the way through, and remove it from the oven.
Set the cake in the pan on a rack to cool for 15 minutes, then turn it out onto the rack. Allow the cake to cool completely, and dust with icing sugar.
Serve with Madagascar vanilla ice cream or whipped cream if desired. Enjoy!