Preheat oven to 180°C/350°F/160°FF
Prepare at 6 cup capacity bundt tin by brushing it carefully with melted butter, then sprinkling with flour, tapping out the excess
In the bowl of a stand mixer, beat the butter, sugar and lemon zest on medium high for 8 minutes, scraping the sides along the way to ensure the mixture is even
Reduce speed and add the eggs, one at a time, mixing well between each addition
Sift together the flour, salt and baking powder and stir the vanilla into the buttermilk
With the mixer on low, add the dry ingredients in 3 parts, alternating with buttermilk and vanilla. Mix until just combined
Pour batter into the bundt tin, tapping the tin to make sure the batter reaches all of the edges.
Bake for 35-40 minutes, until a cake skewer comes out clean. Immediately use a clean linen tea towel to cover the cake and to push it down lightly (this will push down the "dome" on the cake). Rest for 10 minutes, then turn out onto a cake rack to cool