In a large mixing bowl, cream together 1 cup of softened unsalted butter and 1 cup of granulated sugar using an electric mixer. Beat on medium speed for about 3 minutes, until pale and fluffy.

Add 1 large room-temperature egg and 2 tablespoons of lemon zest to the creamed mixture. Mix on low speed until well combined and smooth.

In a separate bowl, whisk together 2.5 cups of all-purpose flour, 2 teaspoons of cornstarch, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt, then gradually add to the wet ingredients.

Gently fold in 1/2 cup of finely chopped fresh raspberries using a spatula.

Drop spoonfuls of 3 tablespoons of raspberry jam onto the dough and lightly swirl it with a butter knife.

Scoop out 2-tablespoon mounds of dough and place them on a lined baking sheet about 2 inches apart.

Preheat your oven to 350°F (175°C) and bake the cookies for 10-12 minutes until they have lightly golden edges.

Allow the cookies to cool on the baking sheet for 5 minutes, then dust with powdered sugar before serving.