Start by preheating your oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper. Lightly flour the sides to prevent sticking.

In a stand mixer fitted with the paddle attachment (or using a hand mixer), cream the room temperature butter and granulated sugar on medium-high speed for 3–5 minutes, until the mixture is light, fluffy, and pale in color.

With the mixer on low speed, add the eggs one at a time, mixing well after each addition. Add in the vanilla extract. Scrape down the sides of the bowl to ensure everything is fully incorporated.

Blend in the sour cream on medium speed until the batter is smooth and creamy. This adds moisture and richness to the cake.

5 In a separate bowl, whisk together the all-purpose flour, cornstarch, baking soda, and kosher salt. With the mixer on low, slowly add the dry mixture to the wet ingredients in batches, mixing until just combined. Don’t overmix stop as soon as the flour disappears.

Divide the batter evenly between the two prepared pans. Smooth the tops with a spatula. Bake for 35–40 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.

For the frosting, beat the softened butter on medium speed until smooth and creamy (about 2 minutes). Gradually add the powdered sugar, one cup at a time, mixing on low. Add in the heavy cream and vanilla extract, then increase the speed and beat for 3–5 minutes until the frosting is light and fluffy.

Once the cakes are fully cooled, spread a generous layer of frosting on the first cake, place the second cake on top, and frost the top and sides. Use an offset spatula for a smooth finish.