Preheat the oven to 325 degrees F. Butter a bundt pan, using 1 tablespoon of butter, on the inside and make sure you cover every nook and cranny. Then sprinkle with some sugar and cover all sides. Turn cake form upside down, to get rid of the excess sugar.

In a bowl, mix cake flour, baking soda, and salt. In second bowl combine buttermilk and orange juice and in a third bowl you'll add the egg whites and whip them until light and foamy. Then add, while the mixer is running, 3 tablespoons of sugar. Mix until you have a thick and glossy consistency. You'll need to stop when you have soft peaks, no stiff peaks.

In a 4th bowl, combine sugar and orange zest and mix with a mixer until the sugar becomes most and starts to cling together (you can use the same mixer attachments as the egg whites) Add the remaining butter and mix until you have a cohesive mixture. Increase the mixer speed and mix until everything is pale and fluffy. At this moment, add the egg yolks, and mix after adding each yolk.

Add 1/3 of the dry mix (cake flour, baking soda and salt) to the sugar/butter mixture and mix. Add half of the buttermilk mixture and mix again. Repeat this and end with 1/3 of the dry mix. Now fold in the whipped egg whites; not all at once, but gradually.

Transfer batter to bundt pan and smooth the top.

Bake in the oven for about 50-60 minutes. Bake until the cake is golden brown and when pressed is bouncing back.

Allow to cool in form for about 10-15 minutes, then remove and allow to cool completely on wire rack.

Make the glaze by mixing sugar, yogurt and orange zest. Drizzle over the cake.