Cake:

1. Preheat oven to 350°F (175°C). Grease and line three 8-inch (20cm) round cake pans with parchment paper.
2. Whisk flour, baking powder, and salt in a bowl.
3. Cream butter and sugar with a mixer until fluffy. Add egg whites one at a time, then mix in vanilla extract.
4. Alternate adding dry ingredients and milk/sour cream, mixing until smooth.
5. Divide batter evenly into pans and bake for 25–30 minutes. Cool completely.

Cranberry Filling:

1. Combine cranberries, sugar, water, and orange zest in a saucepan.
2. Cook over medium heat until cranberries burst and thicken (about 10 minutes). Cool completely.

White Chocolate Frosting:

1. Beat butter until creamy. Add melted white chocolate and mix until smooth.
2. Gradually beat in powdered sugar, heavy cream, and vanilla until light and fluffy.

Sparkling Cranberries:

1. Simmer water and 1/4 cup sugar in a saucepan until dissolved.
2. Toss cranberries in syrup, dry on a wire rack for 1 hour, then roll in remaining sugar to coat.

Assembly:

1. Spread cranberry filling between cake layers.
2. Frost the cake with white chocolate frosting.
3. Garnish with sparkling cranberries for a festive finish.