Preheat oven to 350 degrees F (180 degrees C). Grease and line with parchment a 9x3-inch round cake pan.
Over a sheet of parchment paper, sift together Cake Flour (2 cup), Baking Powder (2 teaspoon), and Salt (1/2 teaspoon). Set aside.
In a large bowl using an electric mixer beat together Granulated Sugar (1 cup), Large Egg (2), and 2 tsp zest of Sunkist Orange (1) until light, creamy and triple in volume, approximately 3-4 minutes.
Lower speed and slowly add Unsalted Butter (1/3 cup) to incorporate. Continue adding Plain Greek Yogurt (1 cup), Grand Marnier (3 teaspoon), and Ground Cardamom (1 1/2 teaspoon).
Add half the sifted flour mixture and half the Orange Juice (1/2 cup) beating until combined. Add remaining flour and remaining juice, beating until smooth - approximately 30 seconds.
Pour into prepared pan and smooth out top. Bake for 37-40 minutes or when a toothpick inserted into center comes out clean.
Combine Grand Marnier (1 tablespoon), Granulated Sugar (4 tablespoon), and Orange Juice (3 tablespoon) juice in a small saucepan and bring to a boil, whisking often. Once at a boil, allow to boil for 2 minutes.
While cake is hot, brush with orange syrup allowing syrup to be absorbed before brushing on more.
Allow cake to cool completely on a wire rack. When cool loosen edges and remove from pan and cut into wedges. Serve with sweetened whipped cream or ice cream.