1. Freeze Nutella Centers

Start by lining a small tray with parchment paper. Dollop 12 heaping teaspoons (around 15–16g each) of Nutella onto the tray. Freeze the Nutella for at least 25–30 minutes, or until solid. This step is essential to maintain the gooey center when baking. If you plan ahead, you can freeze the Nutella centers for up to a few days. Just store them in an airtight container.

2. Prepare the Cookie Dough

• Whisk Dry Ingredients: In a bowl, whisk together the flour, cornstarch, baking soda, and sea salt. Set aside.
• Cream Butter & Sugars: In a mixer, beat together the room temperature butter and both sugars (light brown and granulated) on medium speed for about 2–3 minutes until it slightly lightens in color. You don’t want to over-aerate the dough, as you’re aiming for a denser texture.
• Add Wet Ingredients: Add the egg, egg yolk, and vanilla extract to the butter-sugar mixture. Mix until just combined.
• Combine Dry and Wet Ingredients: Gradually add the dry ingredients to the wet mixture on low speed, mixing until almost combined. There should still be a few flour streaks at this point.
• Optional Add-ins: If you’re using chocolate chips, nuts, or other optional flavorings, fold them in now with a spatula.

3. Chill the Dough (Recommended)

Cover the dough and chill it for 30–60 minutes. This step helps firm up the dough for easier stuffing and improves the overall texture. If you have time, letting the dough rest overnight will develop deeper flavors with subtle toffee notes.

4. Assemble the Stuffed Balls

• Portion the dough into 12 equal pieces (approximately 75–80g each for large cookies, or 20 medium-sized cookies at about 45g each).
• Flatten each piece into a thick disk.
• Place a frozen Nutella puck in the center of each disk and wrap the dough around it, pinching to seal the edges. Be careful to avoid any thin spots that might leak Nutella during baking.
• Shape the dough balls into rough, slightly taller spheres. This helps ensure a thick center once baked.

5. Bake the Cookies

• Preheat the oven to 180°C (350°F) conventional or 170°C (340°F) convection.
• Place the dough balls on a baking sheet lined with parchment or a silicone mat, leaving space for spreading. You can bake 6 large cookies per tray.
• Bake for 10–12 minutes (or 8–9 minutes for medium-sized cookies). The edges should be golden and set, while the centers remain pale and slightly underdone.
• For an extra crinkly texture, try a mid-bake “pan bang” by lifting the tray a few centimeters and letting it drop onto the oven rack. This creates a more textured and rustic edge.

6. Cool the Cookies

Allow the cookies to cool on the baking sheet for 8–10 minutes. This will help the centers finish setting. If you try to move them too soon, the Nutella might spill out. After cooling slightly, transfer the cookies to a wire rack to cool completely.