Preheat Oven to 350°F | 177°C
Grease loaf pan with butter and line with parchment paper. Grease again.
Add to bowl: Gluten Free flour, Pistachio Meal, Cardamom, Baking Powder, Xanthan Guam, and Salt. Set aside.
Second bowl add: Sugar, lemon zest and softened butter. Mix well.
Second bowl add: 3 Eggs and mix well.
Second bowl add: Sour cream and vanilla extract. Mix
Add bowl with the dry ingredients to the bowl with wet ingredients and mix very well.
Pour into the loaf pan. Shake from sided to side to distribute the mix evenly. Pound flat on surface to settle as well.
Place on the top rack of the pre-heated oven and bake for around 60min.It's useful to confirm the temperature of your oven. I have a thermometer I bought for this.
Take out and check with a toothpick or slim knife. If no solids stick to it then it's done.
Let it cool for 15min in the loaf pan.
Leave whole and slice only what you will consume. I think it remains fresher longer.