1. Prepare the oven and dry mixture.
Preheat your oven to 375°F (190°C). In a medium bowl, sift together the cake flour, ½ cup of the sugar, and the cocoa powder, making sure the mixture is smooth and lump-free.

2. Beat the egg whites.
In a large mixing bowl, whip the egg whites with the vanilla extract, cream of tartar, and salt. Continue mixing until the whites form soft peaks.

3. Add the remaining sugar and color.
Gradually beat in the remaining ¾ cup sugar and the blue food coloring. Continue beating until stiff peaks form and the mixture is glossy and thick.

4. Fold in the dry ingredients.
Add the dry mixture about ¼ cup at a time, gently folding it into the egg whites. Avoid stirring—keep folding carefully to preserve the air bubbles.

5. Add blueberries.
Fold in 1 cup of fresh blueberries, distributing them evenly through the batter.

6. Bake the cake layers.
Transfer the batter into two well-greased 9-inch cake pans. Bake for 20–30 minutes or until the tops spring back lightly when touched.

7. Cool the cakes.
Let the cakes rest for 15 minutes, then gently loosen the edges. Flip each cake onto a plate and chill in the refrigerator for 30 minutes to firm the texture.

8. Make the frosting.
In a bowl, blend the softened cream cheese, butter, and vanilla until smooth. Add the powdered sugar and whip until creamy and fluffy. Chill for about 15 minutes.

9. Assemble the cake.
Place the first cake layer onto a serving stand and spread a generous layer of frosting on top. Add the second cake layer and frost the top and sides until fully covered.

10. Finish and serve.
Decorate with the remaining ½ cup of blueberries and serve immediately or chill until ready.