01 - Preheat oven to 325°F. Do not grease a 10-inch chiffon or tube pan.
02 - In a large bowl, sift together cake flour, 1 cup sugar, baking powder, and salt.
03 - In a separate bowl, whisk together egg yolks, vegetable oil, water, vanilla extract, and lemon zest until smooth.
04 - Pour the wet mixture into the dry ingredients and whisk until just combined.
05 - In a clean mixing bowl, beat egg whites and cream of tartar on medium speed until soft peaks form. Gradually add remaining 1/4 cup sugar and continue beating until stiff, glossy peaks form.
06 - Gently fold the egg whites into the batter in three additions, being careful not to deflate the mixture.
07 - Toss blueberries with 1 teaspoon flour to prevent sinking, then gently fold them into the batter.
08 - Pour the batter into the ungreased chiffon pan and smooth the top.
09 - Bake for 45–50 minutes, or until a skewer inserted into the center comes out clean.
10 - Immediately invert the pan onto a bottle or funnel to cool completely for about 1 hour.
11 - Once cooled, run a knife around the edges and center tube to release the cake. Transfer to a serving plate.