In a large bowl, using an electric mixer, beat the butter and sugar on medium speed for about 3 minutes until pale and fluffy. Add the egg and lemon zest, mixing until fully combined.

In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt. Gradually blend the dry ingredients into the wet mixture until a thick dough forms.

Gently fold in the raspberries with a spatula, ensuring even distribution.

Drop spoonfuls of raspberry jam onto the dough and swirl gently with a knife.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Scoop 2-tablespoon mounds of dough on the sheet and bake for 10-12 minutes.

Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack. Dust with powdered sugar before serving.