Finely zest the half lemon, then squeeze its juice.

Whisk 100 g caster sugar, the lemon zest, 56 g butter, and the lemon juice until combined.

Add 1/2 egg, 1/4 tsp vanilla extract, and 1/4 tsp lemon extract.

Whisk the mixture until smooth and fully incorporated.

Add 130 g all-purpose flour, 1/4 tsp baking soda, and a pinch of salt.

Fold the ingredients together until a soft dough forms.

Cover the dough and refrigerate it until firm, for 120 to 180 minutes.

Preheat the oven to 180°C (350°F) and line a baking tray with parchment paper.

Scoop the chilled dough into 8 equal portions.

Roll each dough portion in caster sugar to coat it lightly.

Roll each coated dough portion generously in icing sugar.

Arrange the coated dough balls on the lined baking tray, leaving space between them.

Press a shallow indent into the center of each dough ball with a teaspoon.

Spoon strawberry jam into each indent, using about 3/4 tsp per cookie.

Bake the cookies at 180°C (350°F) for 10 to 12 minutes, until the edges are lightly golden.

Transfer the cookies to a wire rack and cool completely before serving.