3 piping bags fitted with number 2 piping nozzles; a love heart puzzle cookie cutter
For the cookie dough: Preheat the oven to 175 degrees C/350 degrees F. Line a baking sheet with a silicone mat or parchment paper.
In the bowl of a stand mixer, cream the butter and sugar together until the mixture is light and fluffy, about 3 minutes. Add the vanilla extract and egg and beat again for 1 minute to combine, scraping down the bowl to ensure all of the butter mixture is incorporated.
In a separate bowl, mix together the flour, baking powder and salt. With the mixer on low speed, slowly add the dry ingredients in 3 parts and mix until combined.
Scrape the dough onto a work surface and slightly wet your hands. Knead the dough into a smooth disc and place between 2 pieces of parchment paper. Roll the dough out until it is 1/4 inch thick.
Remove the parchment paper and use a heart puzzle cookie cutter to cut out heart shapes. If you do not have a heart puzzle cookie cutter, use a normal heart cookie cutter, then cut the heart down the middle with a knife to create a left and right side. Lift the cookies onto the prepared baking sheet and bake until they are just slightly golden around the edges, about 7 minutes. Allow to cool completely.
For the icing: Add 1 cup of the royal icing mix to one bowl and the remaining 1/2 cup to a second bowl. In the first bowl with 1 cup of icing mix, create the flooding consistency royal icing. Add a drop of red food gel to the bowl and then, starting with 1 teaspoon of water, stir the mixture together with a spoon. Keep adding water to the bowl 1/2 teaspoon at a time until the mixture reaches the flooding consistency--when you drag a line through the icing mixture with a spoon, the line should disappear within 5 to 10 seconds. If the line disappears earlier, your mixture is too runny and you need to add a few tablespoons of royal icing mix to thicken the icing to the right consistency. If the line takes longer than 10 seconds to disappear, then your mixture is still too thick and you need to keep adding water 1/2 teaspoon at a time until you have the correct consistency. Once you have your red flooding icing, place a damp kitchen towel over the top of the bowl to stop it from drying out.
In the remaining bowl, create the soft peak-consistency royal icing. Again, adding just 1/2 teaspoon of water at a time, stir the mixture together until it reaches a soft peak stage--when you lift the spoon out of the bowl and hold it in the air, the icing forms a soft peak on the end of the spoon. If the mixture is too runny and the icing falls off the end of the spoon, add more royal icing mix. If the mixture is too stiff, just add water 1/4 teaspoon at a time and mix together until it reaches soft peak consistency. Once you have the correct consistency, transfer about 2 tablespoons of the white soft peak icing to another bowl. Add red food gel coloring to the remaining mixture and stir to combine. If you would like to flavor any of the royal icing, add 1/4 teaspoon of your favorite extract, such as vanilla.
Transfer the royal icing mixtures into separate piping bags fitted with number 2 round tip nozzles. Cover the ends of the piping nozzles with a damp tea towel at all times to stop them from drying out.
With a cooled cookie in front of you, pipe a border of red soft peak royal icing around the edge of the cookie. Apply even pressure with your hand, and squeeze a thin line of icing along the outside of the cookie, joining the icing up at the end. Repeat on all of the cookies.
Next, you need to flood the cookies. Pipe the red flooding royal icing inside the border you just created on each cookie, filling up the center of the cookies with icing. Use the piping nozzle to squeeze the icing into the edges to ensure each cookie is covered entirely. Allow to set for 10 minutes.
Using the white soft peak royal icing, apply even pressure with your hand and decorate the center of each cookies with names, initials or messages. The cookies should be eaten the same day for the best taste.