Preheat the oven to 180C/350F/Gas 4. Place a baking tray into the oven to heat. Grease a 2.5 litre/4 pint 8fl oz bundt tin (fir tree-shaped, if possible) very liberally with butter.
In a mixing bowl, sift the flour and bicarbonate of soda together.
Mix the butter and sugar together in another large bowl with a wooden spoon (or electric mixer) until light and fluffy.
Add the eggs, one at a time, whisking each one in with a tablespoon of the flour. Carefully fold in the remaining flour using a large metal spoon, then fold in the yoghurt and vanilla extract until well combined.
Pour the mixture into the prepared tin and spread until level. Place the tin on the preheated baking sheet in the oven and cook for 45-60 minutes, until well risen and golden-brown. After 45 minutes, push a metal skewer into the centre of the cake. If it comes out clean, the cake is cooked.
Remove the cake from the oven and place onto a wire rack, without removing it from the tin. Leave to cool for 15 minutes.
Gently pull away the edges of the cake from the tin with your fingers, then carefully turn out the cake onto the wire rack. Leave to cool completely.
Once cool, sieve the icing sugar over the cake. Serve in slices.