1. Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. In a large bowl, whisk together the flour, sugar, baking soda, cocoa powder, and salt.
3. In another bowl, beat the eggs, then add the oil, buttermilk, vanilla extract, vinegar, and purple food coloring. Mix until well combined.
4. Gradually add the wet ingredients to the dry ingredients, mixing until just combined. Be careful not to overmix, as this can affect the cake’s texture.
5. Divide the batter evenly between the prepared pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
6. Let the cakes cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.
7. For the frosting, beat the butter and cream cheese until smooth. Gradually add the powdered sugar and vanilla, beating until fluffy.
8. Once the cakes are completely cooled, spread a layer of frosting on top of one cake, place the second cake on top, and frost the top and sides.

One tip I always remember from my grandmother is to let the cakes cool completely before frosting. It’s a simple step, but it makes all the difference in maintaining the cake’s structure and preventing a frosting meltdown.