Make the Cinnamon Filling

In a small bowl, mix together the softened butter and brown sugar until smooth.

Add the flour, ground cinnamon, and pinch of salt. Mix to form a thick, spreadable filling.

Place in the freezer for 10 minutes to firm up while you make the cookie dough.

Prepare the Cookie Dough

In a large bowl, beat the softened butter and granulated sugar with a mixer until light and fluffy.

Add the vanilla extract, egg, and egg yolk. Mix until fully incorporated.

In a separate bowl, whisk together the flour, baking powder, cornstarch, and salt.

Slowly add the dry ingredients to the wet mixture and mix just until a soft dough forms.

Layer the Dough and Filling

Take half of the cookie dough and press it evenly into the bottom of a large bowl or baking dish.

Retrieve the cinnamon filling from the freezer and dot half of it in small spoonfuls over the dough.

Take the remaining cookie dough and gently press it on top, creating a second layer.

Drop the remaining cinnamon filling over the top of the dough.

Use a spoon or spatula to gently fold and swirl the dough and filling together. Don’t overmix—you want visible cinnamon streaks.

Shape and Chill

Scoop 2-tablespoon portions of dough, ensuring each scoop has both cinnamon and dough.

Place on a plate and freeze for 10 minutes to firm the dough for better baking results.

Bake

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

Arrange the chilled dough balls on the sheets, spacing them apart.

For thick cookies, keep mounds tall.

For flatter cookies, gently press them down.

Bake for 10–12 minutes, until edges are lightly golden. The centers will still look soft—they’ll set as they cool.

Allow to cool on baking sheets set over wire racks.