reheat oven to 350°F. Lightly grease only the bottom of a tube pan or two 9-inch round cake pans
Bring eggs to room temperature by placing them in a bowl of warm water for 10 minutes.
In a large bowl combine dry ingredients: 2 cups cake flour (or all-purpose flour- see notes), 1 1/2 cups granulated sugar, 1 teaspoons salt, and 1/2 teaspoons baking soda. Whisk to fully combine. Sifting removes lumps and lightens the flour for a fluffier crumb.
In a separate bowl, whisk together 0.8 cups fresh orange juice (about 3 large navel oranges), the 6 egg yolks, vegetable oil, melted unsalted butter, and 2 tablespoons orange zest (from the same oranges as the juice) until combined.
Pour the wet mixture into the dry ingredients and whisk until just incorporated and smooth. Do not overmix.
In a clean, completely grease-free glass or metal bowl, beat the 6 egg whites and 1/2 teaspoon cream of tartar on high speed until stiff, glossy peaks form. Any trace of grease or yolk will prevent the whites from whipping.
Gently fold the beaten egg whites into the batter in two or three additions, using a wide rubber spatula. Fold until no white streaks remain, scraping the sides and bottom of the bowl.
Gently spoon (don't pour) the batter into the prepared pan. Drag a butter knife through the batter in a zigzag to release any trapped air pockets.
Bake for 45–45 minutes. until the top springs back when lightly pressed and a toothpick inserted in the center comes out clean. Do not open the oven door before 40 minutes.
et the cake (still in the pan) on a wire rack and cool completely before removing from the pan, about 40–45 minutes.
Run a thin knife around the sides and center tube of the pan to release the cake. Place a serving plate on top of the pan and flip the cake over. Set aside
Make the Orange Glaze