Step 1: Prepare Pans and Preheat Oven

Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans thoroughly with butter or cooking spray. Line the bottoms with parchment paper circles, then grease the parchment. Lightly dust with flour, tapping out any excess. This ensures easy cake release.

Step 2: Sift Dry Ingredients

In a medium bowl, sift together the cake flour, baking powder, and salt. Sifting is crucial for this French Vanilla Butter Cake as it creates an ultra-fine texture. Set aside.

Step 3: Cream Butter and Sugar

In a large mixing bowl using an electric mixer, beat the softened butter on medium speed for about 1 minute until smooth. Gradually add the sugar and continue beating on medium-high speed for 4-5 minutes until the mixture is light, fluffy, and pale in color. This step incorporates air, creating the cake's tender texture.

Step 4: Add Eggs One at a Time

Reduce mixer speed to medium. Add eggs one at a time, beating well after each addition for about 30 seconds. The mixture may look slightly curdled initially—this is normal. Scrape down the sides of the bowl as needed.

Step 5: Incorporate Vanilla

Beat in the vanilla extract and vanilla bean paste (if using) until fully combined. The vanilla is the star flavor of this French Vanilla Butter Cake, so don't skip this important step.

Step 6: Combine Milk and Sour Cream

In a small bowl or measuring cup, whisk together the milk and sour cream until smooth. The sour cream adds moisture and a subtle tang that enhances the overall flavor.

Step 7: Alternate Adding Dry and Wet Ingredients

With the mixer on low speed, add the flour mixture in three additions, alternating with the milk mixture in two additions. Begin and end with the flour mixture. The pattern should be: flour, milk, flour, milk, flour. Mix just until combined after each addition—do not overmix, as this develops gluten and creates a tough texture.

Step 8: Final Mix

Once all ingredients are incorporated, use a rubber spatula to give the batter a final gentle fold, scraping the bottom and sides of the bowl to ensure everything is evenly mixed.

Step 9: Divide and Transfer Batter

Divide the batter evenly between the two prepared pans. Use a kitchen scale for precision if desired. Smooth the tops with a spatula and gently tap each pan on the counter 2-3 times to release air bubbles.

Step 10: Bake

Bake for 30-35 minutes, or until the cakes are golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs. The tops should spring back lightly when touched.

Step 11: Cool in Pans

Remove from the oven and place pans on a cooling rack. Allow the cakes to cool in the pans for 10 minutes. This prevents them from breaking apart when removed.

Step 12: Remove from Pans

Run a thin knife around the edges of each pan. Place a cooling rack over the pan, invert, and gently remove the pan. Peel off the parchment paper. Invert again so the cakes are right-side up. Cool completely before frosting or serving.

Step 13: Serve

Once cooled, the French Vanilla Butter Cake can be served as is with a dusting of powdered sugar, or frosted with your favorite frosting. Slice and enjoy!