• Separate the egg whites into a large, completely clean, and dry glass bowl. Cover and set aside for at least 30 minutes to let the egg whites come to room temperature.
• Sift the sugar 3-4 times and get rid of any hard clumps. Add it to the bowl of a food processor and pulse for 15-30 seconds so it's a very fine texture.
• Measure out 6 tablespoons (¼ cup + 2 tbsp.) of sugar and sift it into a small clean, dry bowl. Set aside.
• Add the cake flour and salt to the remaining 6 tablespoons of sugar that's still in the food processor. Pulse for 15 seconds, then sift them together into a medium clean, dry bowl. Set aside.
• Arrange your oven rack to the second from bottom position. Preheat your oven to 325°F and line a 12-count muffin pan with cupcake liners.
• To the bowl of room temperature egg whites, add the cream of tartar and beat with an electric mixer until thick and foamy, about 1½ minutes. Add the 6 tbsp. granulated sugar and continue to beat for 1½-2 minutes, or until the meringue reaches thick, stiff peaks. You should be able to flip the bowl upside down without the meringue moving at all. Add the vanilla extract and mix until combined.
• Add the dry ingredients to the meringue in 5-6 additions. Use a rubber spatula to gently fold in each addition by wiping the sides and bottom of the bowl and rotating the spatula in towards the middle. Don't add too much of the dry ingredients at once or you'll risk deflating the meringue.
• Once all of the dry ingredients have been added, fold until the batter is combined with no pockets of flour remaining. Don't overmix.
• Use a spoon to scoop the batter evenly into each of the cupcake liners and bake the cupcakes for 18 minutes. Allow to cool slightly before removing them from the pan, then let the cupcakes cool completely before topping with the homemade whipped cream.

Make the Whipped Cream Topping:

• In a large, clean and dry glass bowl, add the cold heavy whipping cream and use an electric mixer to beat until starting to thicken. About 1 minute. Add the powdered sugar, salt, and vanilla extract (if using), and continue to mix until very thick. About 1-2 minutes more.
• Add the whipped cream to a piping bag and pipe it onto the cooled cupcakes. Keep the cupcakes in the fridge until you're ready to serve.