Pre-heat the oven to 180ºC / 350ºF / Gas Mark 4

Grease and line a 23cm / 9" cake tin

Cream the butter and sugar together until pale and fluffy

While the butter and sugar are creaming, sift the flour, bicarb, baking powder and salt, and set to one side

Lightly beat the eggs with the vanilla, and add a little at a time, ensuring each addition is fully incorporated before adding the next

After the last of the egg is added, continue to beat the mixture on full speed for 2 minutes

Turn down the mixer to medium speed, and add a third of the flour, then third of the buttermilk. Repeat until all the mixture is added. Stop mixing as soon as the flour is incorporated

Pour the mixture into the prepared tin and bake for 30 minutes, or until the top is firm and springy and a skewer comes out clean

Let the cake cool a little in the tin until it starts to pull away from the sides. Loosen the cake with a knife around the edges if necessary, then turn out onto a rack to fully cool before decorating