Preheat your oven to 350°F (175°C).
In a large bowl, cream the softened butter and sugar until light and fluffy.
Add the vanilla extract and mix well.
Gradually add the flour and salt, mixing until combined.
Shape the dough into small balls (about 1 inch in diameter) and place them on a baking sheet.
Using your thumb, make an indentation in the center of each ball.
Fill each indentation with your chosen jam or chocolate.
Bake in the preheated oven for 15-18 minutes until the edges are lightly golden.
Remove from the oven and let cool on the baking sheet for a few minutes.
Transfer to a wire rack to cool completely before serving.