Preheat your oven to 350°F (175°C). Line two 8-inch cake pans with waxed or parchment paper. Grease and lightly flour just the paper, leaving the sides ungreased.

In a stand mixer bowl, add cake flour, baking soda, baking powder, salt, and 1 cup of sugar. Mix on low until blended.

With the mixer on low speed, add half of the sour cream and the butter, one tablespoon at a time. Scrape down the sides and bottom of the bowl.

Add the remaining sour cream, oil, and vanilla. Mix on medium speed for about 2 minutes until airy.

In another bowl, whip egg whites with cream of tartar using a whisk attachment until soft peaks form.

Slowly sprinkle in the remaining 1/2 cup sugar, then increase speed until stiff, shiny peaks develop.

Gently fold one-third of the egg whites into the batter until just combined. Repeat this process until all egg whites are incorporated, with slight streaks visible.

Divide the batter evenly between the two pans and gently tap them on the counter to release air bubbles.

Bake for 30-35 minutes until golden brown. A toothpick inserted should come out with slightly moist crumbs.

Allow cakes to cool in the pans for 15 minutes, then turn them out onto a wire rack to cool completely.

In a medium saucepan, bring water to a gentle simmer. Over this, combine egg whites, sugar, water, and cream of tartar in a heatproof bowl.

Whisk often for about 5 minutes until frothy and the sugar dissolves.

Transfer this mixture to the stand mixer. Beat on high until glossy and tripled in volume (around 7 minutes). Add vanilla and any food coloring.

Use this frosting on your cake or cupcakes. It's best enjoyed on the day it's made!