Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, combine flour, sugar, baking powder, and salt. Mix well.

Add softened butter and mix until crumbly.

In another bowl, whisk egg whites, vanilla extract, and milk together. Gradually add to the dry ingredients, mixing until smooth.

Divide the batter evenly between the prepared pans and smooth the tops.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Let cool in pans for 10 minutes, then transfer to a cooling rack.

In a saucepan, combine cranberries, sugar, water, and orange zest. Bring to a boil over medium heat.

Reduce heat and simmer for about 10 minutes until cranberries burst and mixture thickens. Let cool.

In a mixing bowl, beat softened butter until creamy.

Gradually add powdered sugar, mixing until combined.

Add orange juice, orange zest, and vanilla extract. Beat until fluffy and smooth.

Once the cake layers are completely cooled, place one layer on a serving plate.

Spread the cranberry filling evenly over the first layer.

Top with the second cake layer.

Frost the top and sides of the cake with orange buttercream.

Decorate with additional cranberries or orange slices if desired. Slice and serve.