Preheat your oven to 350°F / 175°C.
Grease a 9-inch cake pan, dust it with flour, and line the bottom with a circle of parchment or waxed paper.
In a small bowl, whisk together the egg yolks, 1/4 cup (960 ml) of the sour cream, and the vanilla extract until combined.
Set aside.
In a large separate bowl, add the sifted cake flour, sugar, baking powder, baking soda, and salt.
Whisk vigorously for 30 seconds to combine and aerate the mixture.
Add the softened butter and the remaining sour cream to the dry .
Mix on low speed with an electric mixer until the flour is completely moistened and the mixture resembles coarse crumbs.
Add the egg yolk mixture to the batter in three separate additions, mixing well on medium speed for about 20-30 seconds after each addition until the batter is smooth and creamy. Scrape down the sides of the bowl as needed.
Pour the batter into the prepared cake pan and spread evenly.
Bake in the middle of the oven for 35–40 minutes, or until a toothpick inserted in the center comes out clean. Begin checking for doneness around the 25-minute mark.
Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
