Preheat oven to 350 degrees F (180 degrees C). Trace the circumference of a 9" round cake pan on a piece of parchment paper and cut out the circle. Spray the pan with vegetable spray. Lay the parchment paper on the bottom of the pan and spray again. Set aside.
Zest and segment the Orange (3). Bring the Unsalted Butter (1/2 cup) to room temperature.
Using food processor, pulse Shelled Unsalted Pistachios (3/4 cup) pistachios (3/4 cup) until finely ground, about 40 seconds. Add All-Purpose Flour (1 cup), Baking Powder (2 teaspoon), Ground Cardamom (1 teaspoon), and Salt (1/4 teaspoon). Pulse a few times to combine.
In a large bowl, using an electric mixer on medium speed, beat together softened unsalted butter and Granulated Sugar (1 cup) until light and fluffy (1 1/2-2 minutes). Add Large Egg (3), one at a time, beating well after each addition.
Reduce speed to low and alternate adding pistachio mixture Milk (1/2 cup)-beginning and ending with pistachio mixture and beating just enough to combine. Add orange zest and Vanilla Extract (1/4 teaspoon) and beat just to combine.
Spread batter evenly in a pan and bake until wooden skewer inserted into center of cake comes out clean -- about 30-40 minutes.
Cool in pan and on rack for 10 minutes. Run a knife around cake to loosen it from the pan, and invert onto rack. Peel off parchment paper. It can be served warm or at room temperature with oranges segments and Powdered Confectioners Sugar (to taste).