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

In a stand mixer fitted with a whisk or paddle attachment, beat the room-temperature butter for 2–3 minutes, until light and off-white.

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

Mix in the egg, followed by the vanilla extract, until fully incorporated.

Add the all-purpose flour, cornstarch, cinnamon, baking powder, and baking soda.

Mix on low speed or fold gently just until a soft dough forms—do not overmix.

In a small bowl, mix together the granulated sugar and cinnamon for rolling.

Using a ⅓-cup cookie scoop, portion the dough and roll each ball in the cinnamon sugar mixture.

Place one dough ball per baking sheet to allow for spreading.

Bake for 9–11 minutes, until the edges are lightly golden but the centers remain soft. Slightly underbaking is key for a crisp exterior and gooey center.

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

Beat the butter until fluffy, 2–3 minutes.

Add the powdered sugar and mix until thick and smooth.

Add the heavy cream (or milk), molasses, and vanilla extract, then whip until light and fluffy.

Mix in the cinnamon until evenly incorporated.

Chill the cookies for about 5 minutes. Transfer the frosting to a piping bag or zip-top bag fitted with a round tip (optional).

Pipe a swirl of frosting onto each cookie. Garnish with cinnamon sticks if desired.

Store cookies in the refrigerator for up to 12 days, or at room temperature for up to 8 days.