Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper and set them aside.

Mix in the egg and vanilla extract until well combined. Scrape down the sides of the bowl as needed.

In a separate bowl, whisk together the flour and cornstarch. Gradually add the dry ingredients to the wet mixture, mixing on low speed until a soft dough forms.

Roll the chilled dough into 1-inch balls and place them about 2 inches apart on the prepared baking sheets.

Use your thumb or the handle of a small spoon to gently press two overlapping indentations at the top of each cookie, forming a heart shape.

Spoon a small amount of strawberry jam into the heart-shaped indentation of each cookie. Be careful not to overfill to avoid spillage while baking.

Bake in the preheated oven for 12 - 14 minutes or until the edges are set and slightly golden. Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Once the cookies are cool, serve them as a sweet treat for any occasion or store them for later.