- Position rack in center of oven and preheat to 350 F. Butter 2" deep 9" round cake pan, line bottom with parchment paper, and butter the parchment.
- Whisk flour, baking powder, and salt in small bowl. Combine pistachios and sugar in food processor and process until mixture resembles coarse meal. Add butter and ricotta and pulse until smooth, scraping bowl occasionally. Add eggs and process until smooth, scraping bowl occasionally. Zest half the orange into mixture. Squeeze 2 tbsp juice from orange and add to processor, then add vanilla and process until liquids are incorporated.
- You can add the flour mixture directly and process, or pour liquid mixture into another bowl and hand-mix flour mixture in until everything is incorporated evenly. Pour batter into prepared pan and smooth the top.
- Bake until a toothpick inserted into the center of cake comes out clean, 50-55 mins.
- Cool in the pan on wire rack for 10 mins, then run a thin-bladed knife between the edges of the cake and pan. Invert the cake onto the rack and discard parchment paper. Carefully flip cake again to cool completely on rack.