Preheat the oven to 350 degrees. Line a cupcake pan with paper liners.

Beat the egg whites on high speed until soft peaks form, about 2–3 minutes. Set aside.

Whisk together the flour, cornstarch, baking powder, and salt.

Beat butter on high speed until smooth and creamy, about one minute.

Add the sugar, beating on high until the butter and sugar are creamed together. (3-4 minutes)

Beat on medium-high speed while adding in the egg yolk and vanilla.

Reducing the speed to low, begin to add the dry ingredients. Next, add some of the milk. Alternate with the flour mixture and milk, mixing after each addition and ending with the addition of the flour mixture. Be careful just to blend the ingredients, not overbeat.

Using a spatula, gently fold in the egg whites, pink gel food coloring, and strawberry preserves.

Using a medium ice cream scoop, scoop the batter into the lined cupcake tins.

Bake at 350 degrees for 20–24 minutes, or until an inserted toothpick comes out clean.

Allow to cool in the cupcake pan for about 5 minutes.

Transfer the cupcakes to a wire rack to cool completely.

Cream the butter and powdered sugar until it looks light and creamy.