1-Preheat oven: Preheat oven to 350°F. Grease two or three 8-inch round cake pans and line the bottoms with parchment paper to prevent sticking.

2-Mix dry ingredients: In a large bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt until well mixed.

3-Mix wet ingredients: In another bowl, whisk the eggs, vegetable oil, milk, and vanilla extract until fully combined, creating a smooth wet mixture.

4-Combine wet and dry ingredients: Pour the wet ingredients into the dry ingredients and mix just until combined, being careful not to overmix.

5-Divide batter and color: Divide the batter evenly into six bowls and add a different food coloring to each one red, orange, yellow, green, blue, and purple for those vibrant layers.

6-Prepare pans and refrigerate: Pour one colored batter into each prepared pan and refrigerate the remaining batters while you bake.

7-Bake layers: Bake each layer for about 20 minutes, or until a toothpick inserted comes out clean. Let the layers cool in the pans for 10 minutes, then transfer to wire racks to cool completely. Wash the pans and repeat for the remaining batters.

8-Make buttercream: For the buttercream, beat the softened butter and salt on medium speed until fluffy and pale. Gradually add the powdered sugar and cream, mixing well, then stir in the vanilla extract. Beat until light and fluffy, adding extra cream if needed for the right consistency.

9-Assemble cake: Assemble the cake by removing parchment paper from the cooled layers and stacking them in this order: purple, blue, green, yellow, orange, red. Spread about ½ cup of frosting between each layer.

10-Frost and chill: Frost the entire outside of the cake with the remaining buttercream and chill the assembled cake for at least one hour before serving to set everything perfectly.