Start by preheating your oven to 350°F (175°C). Grease two 9-inch cake pans and line them with parchment paper for easy release. For best results, bring your milk, eggs, and butter to room temperature before you begin.

In a large mixing bowl, sift together the flour, granulated sugar, baking powder, and salt. Whisk briefly to make sure everything is evenly combined.

Drop the cubed, room-temperature butter straight into the dry mixture. Using a stand mixer with the paddle attachment (or a hand mixer), beat on low speed until the mixture looks like coarse, sandy crumbs. This reverse creaming method helps coat the flour with butter, keeping the cake tender and soft.

In another bowl, whisk together the milk, sour cream (or yogurt), eggs, and vanilla extract until smooth and well blended.

With your mixer on low speed, slowly pour in half of the wet mixture. Increase the speed to medium and beat for about 1 minute until the batter looks light and fluffy. Gradually add the remaining wet ingredients and mix until just combined. Be careful not to overmix here.

Divide the batter evenly between the prepared cake pans. Use a spatula to gently smooth the tops for even baking.

Place the pans in your preheated oven and bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean. If you’re making cupcakes instead, they’ll bake in about 18–22 minutes.

Let the cakes rest in their pans for 10 minutes before carefully turning them out onto a wire rack. Allow them to cool completely before adding frosting.

In a large bowl, beat the softened butter on medium speed for about 3 minutes until creamy. Slowly add sifted powdered sugar, one cup at a time, mixing well after each addition. Then pour in the milk (or cream), vanilla, and a pinch of salt. Beat on high for another 2–3 minutes until the buttercream is light, fluffy, and smooth.

Once your cakes are completely cool, spread or pipe the vanilla buttercream as desired. Layer, swirl, and decorate to your heart’s content!