Turban with buttermilk

This recipe is very old. I once received it from a lady who claimed that this would be much tastier and less heavy than the traditional cake.
And it's true, it is very tasty, much less fat and wonderfully airy.
I baked it in an antique, well-cleaned earthenware mold, which gives it even more flavor.

Requirements for the batter:
300 grams of sugar
250ml buttermilk
2 bags of vanilla sugar
3 eggs
350 grams of self-raising flour

Ingredients for the topping:
50 grams of butter
50 grams brown sugar|
50 grams of coconut
cinnamon to taste

Additional needed:
Bundt pan (or cake pan)
mixer or food processor
Butter or oil to grease the pan (I use baking spray)

Preheat the oven to 175 degrees.
Grease the baking tin well.

Beat the sugar, vanilla sugar and eggs until creamy with a mixer or food processor.
Add the buttermilk and stir well.
Beat the self-raising flour into the mixture until fluffy.
Place the turban slightly below the middle in the oven and bake for 40 – 45 minutes.

Meanwhile, for the topping, melt the butter and stir in the sugar, coconut and cinnamon.
After the 40 – 45 minutes, spread this mixture on the turban and put it back in the oven for another 10 minutes.
Insert a toothpick into the turban. If it comes out clean, the cake is done.
Remove it immediately from the mold and let it cool on a rack.