1. Preheat the oven to 350°F and line two baking sheets with parchment paper.

2. In a medium bowl, whisk together the flour, baking soda, and salt.

3. In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy.

4. Mix in the egg and vanilla extract until smooth.

5. Add the green gel food coloring and mix until the dough is evenly colored.

6. Gradually add the dry ingredients to the wet ingredients and mix until a soft dough forms.

7. Scoop the dough into equal portions and roll into balls.

8. Roll each dough ball in the extra granulated sugar to coat the outside.

9. Place the dough balls on the prepared baking sheets, leaving space between each one.

10. Bake for 9 to 11 minutes, until the edges are set and the centers still look slightly soft.

11. Remove the cookies from the oven and immediately press one red heart candy into the center of each cookie.

12. Let the cookies cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.