Preheat oven to 350F.

Line a cookie sheet with parchment paper and set to the side.

In a medium bowl add the room temperature butter and sugar. Cream until blended and crack the large egg in a small bowl and whisk until all combined. Measure out one tablespoon and add to the creamed butter along with vanilla extract and if using lemon zest add it in. Add in the dry ingredients (flour, baking powder, salt) and mix until it begins to form a dough.

The dough will be crumbly. Pour the cookie dough out onto a clean surface and work the dough into a ball.  Divide the dough into two and roll the ball of dough into two smooth balls. Flatten the cookies slowly and with your thumb push into the center of each dough ball to create a heart.  Grab a small spoon and fill the center of the cookie dough with any flavor jam.

Bake cookies on the prepared baking sheet for 8 to 10 minutes. The cookie dough should look firm with very light golden brown sides. Allow the cookies to cool on the baking pan for 5 to 10 minutes before enjoying.

If there are leftovers store them in an airtight container for up to 2 days in the refrigerator.