Preheat the oven to 350°F/180°C. And line 3 half sheet size cookie sheets with ungreased parchment paper or silpat silicone mats (I prefer silicone mats).
In a bowl of a stand mixer, beat the butter with the sugar until creamy (1 minute).
Add the egg and vanilla extract, and beat for 30 seconds, then with a spatula scrape off the sides and the bottom of the bowl and beat for 30 more seconds.
Add in flour and salt, and mix on medium speed until just combined.
Remove 1/3 of the cookie dough to a bowl, add a few drops of food coloring to the rest of the dough (I like to add food coloring with a toothpick), and mix again. Remove half of the dough to a bowl. Add more food coloring to the remaining dough to get a darker color and mix until combined.
To the cookie press add the 3 colors of the dough, and press out hearts on the cookie sheet (if the sheet/silicone mat are greasy, the cookie won’t stick and won’t deattach from the press).
Bake for 8 minutes in the preheated oven, allow to cool for 5-10 minutes then cool completely on a wire rack if needed (these are small thin cookies, they cool quickly).
Notes
To Store: Store in a covered container at room temperature for up to 10 days.
To Freeze: Freeze for up to 2 months, well wrapped in an airtight container.
Decorate with melted white chocolate and sprinkles if desired.