Preheat your oven to 350℉.
In your food processor, pulse your pistachios until they're a crumb, some bigger chunks is ok. In a medium-sized bowl, add the flour, baking powder, salt, and ground pistachios.
In a separate medium-sized bowl, mix together the lemon zest and granulated sugar with your hands, rubbing them together until fragrant.
To the lemon sugar, mix in the eggs, oil, sour cream, and vanilla extract.
Add the mixed dry ingredients into the bowl with the wet ingredients, and mix until just combined.
Spray and line your loaf pan with parchment paper. Pour in the batter and bake for 50-55 minutes.
When the cake is out of the oven and slightly cooled (about 20 minutes), mix together the powdered sugar, lemon, and vanilla extract. Pour over the cake and top with additional pistachios if desired.