Beat sugar, butter, vanilla, and salt until light and fluffy.

Mix in eggs one at a time.

Sift flour, cornstarch, and baking powder into the mixture.

Add half the lemon juice and lemon zest.

Grease and flour a heart-shaped baking pan.

Pour the mixture into the pan and smooth the top.

Bake at 325°F for 30 minutes.

Cover loosely with foil and bake for another 40-45 minutes.

Remove from oven and cool on a wire rack for 10 minutes.

Remove from pan and cool completely.

Beat powdered sugar and egg whites until smooth.

Divide icing; add yellow food coloring to one portion.

Cover the colored icing to prevent drying.

Mix remaining lemon juice with the other portion of icing.

Thin with water if needed.

Spread white icing over the cake and let it dry.

Spoon yellow icing into a piping bag.

Decorate with a large yellow heart and smaller hearts.

Let the icing dry completely.

Serve.