Mix 250 g butter in a large bowl with an electric mixer until creamy. Add Splenda Granulated and lemon zest and mix well. Mix in eggs one at a time. Mix in 1/2 of the flour until combined. Mix in remaining flour until dough becomes one.

Shape dough with your hands into a rectangle. Press flat and wrap in plastic wrap. Refrigerate for 2 hours.

Preheat the oven to 180°C. Line 2 baking sheets with parchment paper.

Dust a work surface with flour and roll out dough into a thin circle. Cut out heart shapes (you can also use a heart shaped baking mold) and arrange the cookies on the prepared baking sheets.

Bake in the preheated oven until lightly browned, 10 to 15 minutes. Remove hearts from baking sheets carefully and transfer to wire racks. Set aside to cool completely.

Beat egg whites in a bowl until frothy. Beat in Splenda Granulated 1 tablespoon at a time, until stiff peaks form. Add lemon juice to thin out the mixture. Add more lemon juice for runnier icing. Add red food colouring based on preferred icing colour and spread this on the cooled cookies.