Preheat the oven to 180°C/160°C Fan/gas mark 4/350ºF and put a baking sheet in at the same time. Butter or oil your large, regular or fir-tree shaped bundt tin (2.5 litres capacity / 2½ quart capacity) very, very thoroughly. (I use oil-sodden kitchen paper.)Either by hand or in a freestanding mixer, cream together the butter and sugar until light and fluffy.Add the eggs one at a time, whisking each one in with a tablespoon of flour.Fold in the rest of the flour, and add the bicarbonate of soda, the yogurt and vanilla extract. Don't overbeat or the cake will rise too much, giving an overly-domed bottom later - though it's not the end of the world, as you can always trim it if necessary.Pour and spoon the mixture into your greased tin and spread about evenly.Place the tin on the preheated baking sheet in the oven and cook for 45–60 minutes until well risen and golden. After 45 minutes, push a skewer into the centre of the cake. If it comes out clean, the cake is cooked. Let it sit out of the oven for 15 minutes. Gently pull away the edges of the cake from the tin with your fingers, then turn out the cake, hoping for the best.Once cool, dust with the icing sugar pushed through a small sieve, to decorate: think fresh snowfall on the alps.