Preheat your oven to 350°F (175°C). Gather your tools: a 10-inch ungreased tube pan, a mixing bowl, and an electric mixer.

In a large bowl, sift together all-purpose flour and cornstarch five times to aerate. Then sift the sugar and salt mixture into the flour blend two more times.

Beat the room-temperature egg whites in a clean bowl until foamy, about 1-2 minutes. Add cream of tartar, vanilla extract, and lemon zest, then gradually add remaining sugar until stiff peaks form.

Gently fold in the flour mixture in four batches. Toss blueberries in a little flour before folding them into the batter.

Pour the batter into your ungreased tube pan and bake for 40-43 minutes until golden brown.

Invert the pan immediately onto a bottle or a wire rack to cool upside down for about 2-3 hours.

Mix lemon juice with powdered sugar in a small bowl until smooth. Set aside until the cake has cooled completely.

Once cooled, remove the cake from the pan and pour the glaze over the top. Garnish with lemon slices.