Prepare the Dough: In a spacious mixing bowl, blend marzipan and powdered sugar together, stirring until the mixture is smooth and well combined. Add the egg white, ground almonds, cinnamon, amaretto, and salt, stirring until well incorporated. Gradually fold in the flour to form a sticky dough.

Chill the Dough: Wrap the dough in plastic wrap and place it in the refrigerator for 30 minutes to make it more manageable.

Form the Cookies: Preheat your oven to 180°C (350°F) and prepare a baking sheet with parchment paper. Once chilled, roll the dough into small balls, roughly 1 inch in diameter, and arrange them on the baking sheet, leaving a little space between each. Gently flatten each ball using your fingers.

Decorate the Cookies: Brush the tops of the cookies with beaten egg yolk. Sprinkle slivered almonds on each cookie, pressing them lightly to adhere.

Bake the Cookies: Place the cookies in the preheated oven and bake for 12 to 15 minutes, or until the edges are a light golden brown. Lift the cookies from the baking sheet and let them cool for 5 minutes before moving them to a wire rack to cool completely.

Serve and Store: Enjoy these cookies fresh or store them in an airtight container for up to a week.