To Make the Cake Layers:

1. Preheat Oven: Preheat the oven to 350°F. Line four 9-inch cake pans with parchment paper and spray with nonstick cooking spray.
2. Mix Butter and Sugar: Cream the butter and sugar together for 5-6 minutes until light and fluffy.
3. Add Eggs: Add the eggs one at a time, beating well after each addition.
4. Add Dry Ingredients: On low speed, gradually add flour, salt, baking powder, then the milk and vanilla. Mix until well combined.
5. Bake: Divide batter among the pans and bake for 25-30 minutes, or until tops spring back when lightly pressed. Cool completely before decorating.

To Make the Buttercream:

1. Combine Ingredients: Mix egg whites, powdered sugar, and salt on low speed until combined.
2. Add Butter: Gradually add butter, beating on medium speed until light and fluffy.
3. Flavor: Add vanilla extract and mix for another minute.

To Assemble and Decorate:

1. Cut Cake Rounds: Cut each cooled cake round in half to create 8 layers. Stack with frosting between layers, tinting frosting in shades of yellow and orange for an ombre effect inside.
2. Crumb Coat: Apply a thin layer of white frosting to seal crumbs and refrigerate for 1 hour.
3. Stencil Decoration: Use a parchment stencil on the chilled cake, apply sanding sugar in an ombre pattern, and cover the top with orange sanding sugar.
4. Finish: Remove the stencil and add candies around the base.