Preheat your oven to 325°F (160°C). Ensure your chiffon cake pan is clean and ungreased.
In a large mixing bowl, sift together the cake flour, sugar, baking powder, and salt. Set aside.
In another bowl, whisk together the vegetable oil, egg yolks, cold water, vanilla extract, and orange extract until well combined.
Pour the wet ingredients into the dry ingredients and mix until smooth. Be careful not to overmix.
In a clean mixing bowl, beat the egg whites with cream of tartar until soft peaks form. Gradually add in the remaining sugar and continue to beat until stiff peaks form.
Gently fold the whipped egg whites into the batter, one-third at a time.
Pour the batter into the ungreased chiffon cake pan. Bake for 50-60 minutes, or until a toothpick comes out clean.
Once baked, invert the cake pan onto a cooling rack and allow the cake to cool completely in the pan.
While the cake cools, prepare the frosting by beating the softened butter until creamy. Gradually add the powdered sugar, orange juice, orange zest, and vanilla extract until smooth.
Once the cake is completely cool, gently remove it from the pan and frost with the orange buttercream frosting. Optionally, garnish with fresh fruit.