Preheat your oven to 350°F (177°C).

Grease two 8- or 9-inch round cake pans with oil, butter, or cooking spray. Add a small amount of flour, tilting and tapping the pan to evenly coat all surfaces. Tap out excess flour.

In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt. Set aside.

In a large bowl or stand mixer, beat softened butter and sugar on high speed for about 3 minutes until creamy, scraping down the sides as needed.

Lower mixer speed to medium-high and add egg yolks one at a time, followed by vanilla extract, beating until well combined.

Gradually add dry ingredients and buttermilk to the creamed butter mixture, alternating between the two and mixing on low speed until fully incorporated. Stir by hand to ensure no lumps remain.

In a clean bowl, beat egg whites and cream of tartar on high speed until fluffy peaks form, about 3 minutes. Gently fold into the cake batter to keep it light and airy.

Divide the batter evenly between the prepared pans. Bake for 22-25 minutes, or until a toothpick inserted into the center comes out clean. Remove cakes from oven and cool completely.

While cakes are cooling, make the caramel icing: In a large saucepan over low heat, melt the butter.

Add evaporated milk, sugar, and salt. Stir to combine.

Cook on low to low-medium heat, whisking every few minutes with a sauce whisk for about 1 to 1 ½ hours, monitoring consistency until it thickens enough to coat the back of a spoon and turns a golden brown.

Remove the caramel icing from heat and stir in the vanilla extract.

Let the caramel cool for 15 to 20 minutes before pouring it over the cake.