Preheat the oven to 350°F (convection) and line a baking sheet with parchment paper.

In a stand mixer or with a hand mixer, beat the room-temperature butter for 3–5 minutes, until pale and off-white.

Add the brown sugar and granulated sugar. Beat for about 2 minutes, until the mixture is light and fluffy.

Mix in the egg until fully incorporated.

Add the vanilla extract, corn syrup (optional), and molasses (optional), mixing until smooth.

Mix on low speed (or fold by hand) just until a thick dough forms.

Scoop ⅓-cup portions of dough and place one test cookie on the baking sheet.

Bake to check dough spread and confirm oven temperature before baking the full batch.

Once the test cookie looks right, place remaining dough balls on the baking sheet, spacing evenly.

Bake for 11–12 minutes, until the edges are set and the centers remain soft.

Immediately after baking, use a round bowl or cup to gently swirl around each cookie to create clean, circular edges.

Let cookies rest on the baking sheet for about 10 minutes, then transfer to the refrigerator to cool completely before frosting.

Beat the butter and shortening together until light and off-white.

Gradually add the powdered sugar until fully incorporated.

Add the heavy cream (or 2 tablespoons milk, if substituting) and extracts, then whip until light and fluffy.

Optional: Gently fold with a spatula to remove air bubbles before piping.

Transfer frosting to a piping bag, zip-top bag, or spread with a knife.

In a small bowl, mix the cocoa powder with the heavy cream to deepen the chocolate color.

Add the chocolate and milk mixture to a heat-safe bowl and microwave in 30-second intervals, stirring between each, until smooth.

Pour the melted chocolate onto a parchment-lined tray, spread evenly, and top with sprinkles.

Freeze for 20–30 minutes, then break into chunks.

Frost the chilled cookies and top with pieces of chocolate bark.

Store cookies in the refrigerator for up to 10 days, or at room temperature for up to 8 days.