Preheat your oven to 350°F (175°C). Sift together all-purpose flour and cornstarch five times into a large bowl.

In another bowl, whisk together 3/4 cup of sugar and a pinch of salt. Sift this mixture into the flour blend two more times.

Beat the egg whites using an electric mixer on medium speed until foamy, about 1-2 minutes.

Add cream of tartar, vanilla extract, and lemon zest to the foamy egg whites. Continue beating until it holds soft peaks, about 2-3 minutes.

Slowly add the remaining sugar, about 1 tablespoon at a time, and beat until stiff peaks form, about 10-13 minutes.

Carefully fold in the flour mixture in four parts using a spatula.

Toss the blueberries with a tablespoon of flour to coat and gently fold into your batter.

Pour half of the batter into an ungreased tube pan. Add half of the blueberries, then layer on the remaining batter and top with the last of the blueberries.

Bake for 40-43 minutes, until the top is golden brown and springs back when touched.

Invert the tube pan onto a neck of a bottle to cool for 2-3 hours upside down.

Run a knife around the edges of the pan, invert the cake onto a serving plate, and gently tap to release.

Whisk together lemon juice and powdered sugar until smooth. Adjust consistency with water if necessary.

Pour the glaze over the cooled cake and garnish with lemon slices. Let it set for 15-20 minutes before slicing.