Preheat oven to 350°F (175°C). Have an ungreased 10-inch tube pan ready. Do not use a non-stick pan.

In a medium bowl, sift the cake flour and salt together three times. Set aside.

In a large, perfectly clean glass or metal bowl, beat the room-temperature egg whites on medium speed until foamy. Add cream of tartar and continue to beat until soft peaks form.

While mixing on low speed, gradually add the granulated sugar, one tablespoon at a time. Add lemon zest and vanilla extract. Increase speed to medium-high and beat until stiff, glossy peaks form.

Gently sift one-third of the flour mixture over the egg whites. Using a rubber spatula, gently fold it in. Do not stir. Repeat with the remaining flour in two more additions.

Gently fold in the floured blueberries until just integrated.

Carefully spoon the batter into the ungreased tube pan and gently level the top. Do not tap the pan.

Bake for 35 to 45 minutes, or until the top is golden brown, springs back lightly when touched, and a wooden skewer comes out clean.

Immediately invert the pan onto a wire rack to cool completely, upside down. Allow to cool for at least 1 1/2 to 2 hours.

Once completely cool, run a thin knife around the outer and inner edges of the pan to release the cake. Place the cake right-side up on a serving platter.

Whisk together the powdered sugar, lemon juice, lemon zest, milk, and vanilla extract until smooth. Drizzle generously over the cake. Garnish with extra blueberries and serve.