Preheat oven to 325°. Grease and tap sugar into a 10 inch bundt pan or 2 standard size loaf tins.
Measure out flour, sugar, baking powder, and salt into a mixing bowl. Stir thoroughly, about 30 seconds. Low speed setting.
In a separate bowl, whisk together eggs, vanilla extract, and buttermilk. Whisk only to incorporate the eggs but don't beat too hard or you will add unnecessary air into the mixture. Set aside
Juice lemons for 4 Tbsp, about 3 Lemons. Zest lemons for 2 Tbsp, about 6 lemons. You can put the juice and zest in the same bowl, set aside.
Cut the butter into smaller pieces and place into large mixing bowl with the dry ingredients.
Cream the butter and the dry ingredients until well incorporated. It will look like lightly damp sand. This is the only time you should use a higher speed setting.
Add half the egg and buttermilk mixture and mix well. Low speed setting.
Add the final half of the egg mixture and mix well. Low speed setting.
Add the lemon juice and zest and mix well. Low speed setting.
Pour batter into the bundt pan or evenly between to two loaf tins and bake.
Cakes will need about 65 minutes in the oven but check regularly at the 55 minute mark.
Once the cake is out of the oven, run a blunt knife around the edges of the pan to loosen the cake. Let it cool in the pan for about 10 minutes before turning it out onto a cooling rack. Allow it to cool for a minimum of 30 minutes.