In a large bowl, beat the softened butter and caster sugar together until pale and fluffy.

Mix in the egg and vanilla extract until the mixture is smooth and well combined.

Gradually add the flour to the mixture, stirring until a soft dough forms. If desired, add lemon zest or almond extract for added flavor.

Cover the dough with plastic wrap and refrigerate for 20 to 30 minutes to firm it up.

Preheat your oven to 350°F (175°C).

Roll tablespoon-sized portions of dough into balls and place them on a lined baking sheet.

Using your thumb or the back of a spoon, press into the center of each ball to create a well.

Spoon about ½ teaspoon of raspberry jam into each indentation.

Bake the cookies in the preheated oven for 12 to 15 minutes, or until lightly golden.

Remove the cookies from the oven and let them cool on a wire rack. Dust with powdered sugar before serving if desired.