Preheat oven to 180°C. Grease 2 baking trays. Line with baking paper.
Using an electric mixer, beat butter, sugar and vanilla until light and fluffy. Add egg yolk. Beat to combine. Add flour. Stir to combine.
Roll 2 tablespoons of mixture into a ball. Repeat with remaining mixture to make 10 balls. Place balls 10cm apart on trays. Using the palm of your hand, flatten each ball to form a 7cm round, shaping edges to remove any cracks.
Gently press a 5cm heart-shaped cutter into the centre of each round, being careful not to cut the whole way through. Using the tip of a small knife, scoop out the dough to make a heart shaped indentation. Gently smooth indentation. Fill each heart with 2 teaspoons jam, spreading out to edges. Bake for 15 to 20 minutes or until light golden. Cool on trays. Serve.