Preheat the oven to 190°C (375°F) and line a baking sheet with parchment paper.

Cream together the butter and brown sugar with an electric mixer until light and fluffy.

Add the egg and vanilla extract, mixing until incorporated.

Add the flour and salt, blending until a soft dough forms.

Roll the dough into 1-inch balls and place them on the prepared sheet.

Gently press your thumb or the rounded back of a teaspoon into the center of each ball to form a heart-shaped indent.

Bake for 12–15 minutes, until the edges are lightly golden and the centers look set.

Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Gently reshape the indents if filled in while still warm.

Once cooled, spoon a small dollop of jam into each heart-shaped center.