Preheat your oven to 350°F and line a large baking sheet with parchment paper or a silicone baking mat to ensure the cookies don't stick.

In a large mixing bowl, cream together the softened butter and lightly packed brown sugar until the mixture is light, fluffy, and smooth.

Add the egg and vanilla extract to the butter mixture and beat well until fully incorporated and the batter looks pale.

Gently stir in the all-purpose flour and salt using a spatula or wooden spoon until a soft dough forms and no white streaks remain.

Scoop about one tablespoon of dough at a time and roll it into a smooth ball between your palms before placing it on the prepared baking sheet.

Use your thumb or the back of a small measuring spoon to press two diagonal indents into the center of each ball to create a heart shape.

Carefully fill each heart-shaped indentation with a small amount of jam using a teaspoon or a small piping bag for precision.

Bake the cookies for 10 to 12 minutes or until the edges are just barely golden brown and the centers feel set to the touch.

Allow the cookies to cool on the baking sheet for at least five minutes before transferring them to a wire rack to cool completely.