Preheat oven to 350°F. In a medium bowl, whisk together flour, baking powder, and salt.
In a large mixing bowl or the bowl of a stand mixer, cream butter and cane sugar together until pale in color. Whisk in egg whites until batter is smooth.
Fold in half the dry ingredients, then half the buttermilk and repeat. Fold in lemon zest and juice.
Line two cupcake pans with cupcake liners and fill ⅔ full of batter. Bake for 20 minutes (rotating pans halfway through baking) or until a toothpick inserted in the centers come out clean. Set aside to cool completely.
Cream butter and add sifted confectioner's sugar. Beat frosting until smooth then mix in ½ cup of strawberry jam. Place in a piping bag fitted with a star piping tip.
To decorate cupcakes, pipe frosting in a circular pattern over the top of the cupcake leaving a well in the center. Place a teaspoon of strawberry jam in the center of the frosting. Top cupcakes with a strawberry half.