Preheat oven to 350 F degrees and lightly grease three 8" round cake pans with nonstick cooking spray and line with parchment paper rounds.
Also, lightly grease the tops of the paper in the pans.
Sift together flour, salt and baking soda and set aside.
In the bowl of a stand mixer, fitted with the paddle attachment, cream the butter and 1½ cups sugar together until smooth and no lumps of butter remain.
Add the vanilla and 7 egg yolks and mix until just combined, scraping down sides of the bowl if necessary.
Slowly add sifted dry ingredients and sour cream, alternating between the two until fully combined.
Mix until batter is light and fluffy, about 3 to 5 minutes, then transfer batter to a large mixing bowl.
In a clean bowl of a stand mixer, fitted with the whip attachment, beat the remaining 7 egg whites, cream of tartar, and remaining ¼ cup of sugar on high speed until tripled in volume and soft, but not dry, peaks form.
Gently fold the whipped egg whites into the batter, in two additions.
Spread the batter into the prepared pans and bake until light golden brown and knife inserted into cake comes out clean, about 30 minutes.
Let the cakes cool on rack for about 20 minutes, then carefully turn the cakes out of the pans on onto a rack to cool completely before frosting.
For the Earl Grey Pastry Cream.
In a medium saucepan, bring the milk, vanilla bean, Earl Grey tea and ½ cup of sugar to a boil. In a large bowl, whisk the eggs, yolks, cornstarch and ¼ cup sugar until smooth and set aside.
Slowly pour the hot milk over the eggs, while whisking constantly, until fully combined. Return the entire mixture to the pot and cook over low heat until thickens and bubbles rise to the surface, while stirring constantly.
This happens quickly so don’t take your eyes off it.
Remove from heat and strain the pastry cream through a fine-mesh sieve into a shallow dish, add the butter and whisk smooth.
Cover the surface directly with plastic wrap, and refrigerate until chilled and set.