Beat butter and sugar in a stand-up mixer, using the paddle attachment. If using coconut sugar, mix for 3-4 minutes until it's nice and creamy. I like to use the 2 or 4 setting.
Add the eggs, one at a time, mixing until they are all combined.
Next, add all the liquids - sour cream, buttermilk, lemon juice and vanilla. Mix until nice and creamy.
Now, add the dry ingredients - flour, arrowroot powder, baking powder and salt. Mix until thoroughly combined.
Lastly, fold in the lemon zest.
Pour the batter into a greased 8x4 pan. Alternatively, use parchment paper as a liner. It can also be easier to pull the loaf out once it is done cooling
Bake in a 325° oven for 60-70 minutes. Insert a toothpick or cake tester to tell it it's done. If you see cake batter still on the tester, place it back in for five or six minutes.
Allow to cool and then release the loaf from the pan.
