Step 1

Preheat the oven to 325°F. Line 2 (12-cup) muffin tins with 16 cupcake liners.

Step 2

In a food processor, add the sugar and process until very fine and almost powdery, about 1 minute. Remove and reserve ½ cup of the fine sugar.

Step 3

In a sifter over a large bowl, combine the remaining fine sugar, cake flour, and salt. Sift together, then whisk until well combined.

Step 4

In a large mixing bowl or the bowl of a stand mixer, beat the egg whites, warm water, and cream of tartar on medium-low speed until frothy, about 1 minute. Increase the speed to medium. Gradually add the reserved ½ cup of fine sugar, a tablespoon at a time, beating until stiff peaks form, about 4 minutes total. (You do not need to keep beating until they are glossy.)

Step 5

Sift in a quarter of the flour mixture into the egg whites and gently fold until just combined. Repeat with the remaining flour, adding in three more batches. Divide the batter evenly among the cupcake liners, filling to the top of each liner (about ⅓ cup or 25g each). Use a spoon or spatula to gently even the tops of the batter.

Step 6

Bake for 25 to 30 minutes or until the tops are golden brown and firm to the touch in the center. Let the cupcakes cool completely in the pan.

Step 7

In a large mixing bowl, beat the cream, sugar, and vanilla on medium-high speed until stiff peaks form, about 3 minutes. Pipe or dollop the whipped cream on top of the cooled cupcakes. Garnish with fresh berries, if desired.