Preheat oven to 350F. Line baking sheet with parchment paper and set aside.
In a large stand mixer using the paddle attachment or large bowl with hand mixer, cream butter and sugar for 1-2 minutes. It will begin to get fluffy and will change to a lighter colour.

Add the egg yolk with vanilla extract and mix well. Then add the flour and salt and mix until just combined. Make 12 cookie dough balls.
Using the tip of a spoon or your thumb, immediately press the centers of the cookies down in a criss cross to make a small heart shape.

#Tips:
Keep in airtight container up to two weeks.