In a large mixing bowl, use an electric mixer to beat together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda and salt.
Gradually add the flour mixture to the wet mixture and mix until just combined.
Fold in the chopped chocolate and walnuts.
Divide the marzipan into small, bite-sized pieces and roll each piece into a ball. Place them in a dish with 1–2 teaspoons of flour, gently rolling to coat and prevent sticking. Fold the marzipan pieces into the dough, mixing just until they’re evenly distributed
Cover the dough and let it sit for 30 minutes at room temperature.
Preheat the oven to 375°F (190°C) and line several baking sheets with parchment paper.
Portion out balls using approximately 2 tablespoons (50 grams) of dough each. Place them on the prepared baking sheets 2 inches (5 cm) apart. They will flatten as they cook.
Bake for 10 minutes at 190°C or until golden brown around the edges. Let the cookies rest on the baking sheet for 10 minutes and then transfer to a wire rack to cool completely.
