1. Prepare the dry ingredients

• Sift cake flour, baking powder, salt, and 3/4 cup of sugar into a large mixing bowl.

• Mix gently to combine and set aside.

2. Mix the wet ingredients

• In a separate bowl, whisk egg yolks, oil, blueberry puree, water, vanilla extract, and lemon zest.

• Beat until smooth and fully combined.

3. Combine wet and dry mixtures

• Add the wet ingredients into the dry flour mixture.

• Whisk gently until you get a smooth, lump-free batter.

• Do not overmix to keep the batter light.

4. Whip the egg whites

• In a clean, dry bowl, beat the egg whites until frothy.

• Add cream of tartar and continue to beat.

• Gradually add the remaining 3/4 cup sugar while beating.

• Whip until stiff peaks form, but do not overbeat.

5. Fold the egg whites

• Add a third of the whipped egg whites to the batter and gently fold to lighten the mixture.

• Fold in the remaining egg whites in two batches.

• Use a spatula and a gentle folding motion to preserve the airiness.

6. Add optional whole blueberries

• If using whole blueberries, toss them lightly in flour to prevent sinking.

• Gently fold them into the batter before pouring into the pan.

7. Bake the cake

• Pour batter into an ungreased 10-inch tube pan.

• Smooth the top lightly with a spatula.

• Bake at 325°F (160°C) for 50–55 minutes until a skewer comes out clean.

8. Cool the cake

• Invert the pan immediately after baking and let the cake cool upside down in the pan.

• Cool completely before loosening the edges with a knife and removing from the pan.

9. Serve and garnish

• Dust the cooled cake with powdered sugar or drizzle with lemon glaze.

• Slice gently with a serrated knife to preserve texture.

• Serve with whipped cream and fresh berries if desired.