Preheat oven to 375F, with a rack in the center of the oven. If using a tub pan without removeable bottom, cut a piece of circular parchment to fit the bottom of the pan.
In a large bowl, sift the cake flour and 150g of sugar together. Repeat one more time, for a total of two siftings. Set aside.
In the bowl of a stand mixer or a large bowl to accomodate a hand beater, beat the egg whites and cream of tartar on medium until foamy. Then add the 200g of sugar, 2 TB at a time, until a soft meringue forms. Beat the meringue on high to stiff, but not dry, peaks. If you beat too much, a dry meringue will make folding the flour/sugar mixture in difficult.
Add the vanilla, and then stop beating.
Sprinkle 1/3 of the sifted flour/sugar over the meringue, and fold until combined, working swiftly and confidently. Repeat with another 1/3, and then the last 1/3.
Gently pour the batter into the tube pan. Level the batter out, and then run a butter knife or offset spatula through the middle circumference to eliminate any large air bubbles. Run your thumb around the outer edge of the cake batter.
Bake for 35-40 minutes, until the cake is golden brown and firm-springy to the touch. Remove from the oven, and cool upside down. The cake won't fall out, so don't worry!
Once completely cool, run a offset spatula around the outer and inner portion of the tube pan, and release the cake onto the desired serving platter.
To ice, mix powdered sugar and lemon juice to a drizzling consistency. Pour over cake. Shower over sprinkles. Cake will keep well-wrapped at room temperature for up to 4-5 days.