Heat oven to 325°F. Line two baking sheets with parchment.
Grate the marzipan on large holes and set aside.
Cream butter and powdered sugar until light and fluffy, about 2 minutes.
Beat in grated marzipan until mostly smooth.
Mix in vanilla, almond extract, salt, and orange zest.
Whisk flour and cornstarch together in a small bowl.
Add dry ingredients to the mixer on low. Mix just until a soft dough forms.
Chill dough 15–20 minutes to firm slightly for easier shaping.
Scoop heaping tablespoons of dough and roll into balls. Space 2 inches apart on sheets.
Flatten each ball to 1/2 inch thick. Top with sliced almonds and sparkling sugar, pressing gently.
Bake 14–16 minutes, until edges turn pale golden and centers are set.
Cool 5 minutes on the sheet, then move cookies to a rack to finish cooling.
Melt chocolate and drizzle over cooled cookies, if desired. Let set before serving.
Notes
Variation: Add a pinch of cardamom to the dough, or dip half the cooled cookie in melted dark chocolate. Storage: Keep airtight at room temperature up to 5 days, or freeze baked cookies for 1 month.This recipe is an original creation inspired by classic Marzipan Shortbread Cookies Recipe flavors. All ingredient ratios and instructions are independently developed.