In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed for about 30 seconds.
⅔ cup salted butter
Add the sugar to the bowl and mix until light and fluffy. Scrape down the sides of the bowl to ensure a smooth mixture with no grain.
½ cup granulated sugar
Add the egg yolks and vanilla and mix until combined.
2 large egg yolks, 1 teaspoon pure vanilla extract
In a separate, medium bowl, whisk the flour and cornstarch together.
1½ cups all-purpose flour, 1 teaspoon cornstarch
Gradually add the dry mixture to the bowl and mix on low speed until incorporated. Use a silicone spatula to scrape the bowl and combine.
Cover the bowl with plastic wrap and chill for 1 hour in the refrigerator.
After the dough has chilled, preheat oven to 350°F and line 2 baking sheets with parchment paper.
Using a medium cookie scoop or tablespoon, scoop the dough and roll it into balls with your hands. Place 12 balls about 1 inch apart on each baking sheet.
Using the end of a small spoon (I used espresso spoons) or your thumb gently press a heart shape into the balls.
Fill each heart cavity with about 1⁄2 a teaspoon of strawberry jam.
⅓ cup strawberry jam or preserves
Chill the cookies for 10 minutes in the freezer.
Bake for 12-14 minutes, or until they are golden on the bottom.
Leave cookies on the baking sheet for 5 minutes and then transfer them to a cooling rack. Once cool serve and enjoy with your favorite beverage.