Take out ingredients from the fridge at least two hours in advance - e.g., butter, eggs, yogurt.

Line the baking pan with parchment paper or grease with butter and sprinkle with breadcrumbs or flour.

Preheat the oven to 170℃ in convection mode or 180℃ in top/bottom heat mode.

Sift together the flour, baking powder, and salt (if using).

Transfer butter, sugar, and vanilla to the mixer bowl.

Beat together until combined, pour in the oil and beat on high speed.

Beat for several minutes until the mixture becomes light in color and significantly increases in volume.

Then add eggs one by one to the mixture (I add a tablespoon of sifted flour immediately with each egg) and beat each briefly on low speed.

Add about half of the remaining flour to the mixture and beat very briefly.

Add yogurt and beat briefly.

Add the rest of the flour and combine briefly - stop mixing when you can still see remnants of flour on the sides of the bowl.

Then just fold in the batter with a spoon.

Transfer about 1/2 of the batter to another bowl.

Add cocoa and cinnamon to it - mix.

In the prepared pan, alternately layer vanilla batter and cinnamon batter.

Finally, gently swirl the batter with a knife or skewer to combine the mixtures.

Place the pan with the batter into the preheated oven and bake for about an hour - until a dry skewer comes out clean.

After baking, cool the cake completely.

Sift powdered sugar into a bowl, add cinnamon and milk, one tablespoon at a time - mix until you get a slightly runny, but still thick icing.

Spread the icing over the top of the cake.