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 and mix well. Then add the flour and salt and mix until just combined.

Make 12 cookie dough balls and then roll into additional sugar.

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. If you wait too long to press down the cookies will start to crack.

Fill the hearts with jam and bake cookies for 12-15 minutes on the prepared baking sheet. The edges will just begin to brown.

Let cookies cool on cookie sheet for 5 minutes then transfer them to a wire rack to finish cooling. Enjoy!