Portion the Nutella: Line a small plate with parchment. Drop 10–12 teaspoon-sized dollops of Nutella onto the parchment. Freeze for 30–45 minutes, until firm. This makes stuffing easy and mess-free.

Cream the butter and sugars: In a mixing bowl, beat softened butter, granulated sugar, and brown sugar until light and fluffy, about 2–3 minutes. This step builds structure and helps with chewiness.

Add egg and vanilla: Beat in the egg and vanilla until smooth and glossy. Scrape down the bowl to ensure everything is well combined.

Whisk dry ingredients: In a separate bowl, whisk flour, baking soda, baking powder, and salt. Add dry ingredients to the wet mixture and mix on low until just combined. Do not overmix.

Fold in extras: If using chocolate chips or hazelnuts, fold them in gently. The dough should be soft but not sticky.

Chill the dough: Cover and chill for at least 30 minutes. Chilled dough is easier to handle and holds its shape better in the air fryer.

Form the cookies: Scoop about 2 tablespoons of dough (a heaping medium cookie scoop). Flatten into a disc in your palm. Place a frozen Nutella dollop in the center. Wrap dough around it and pinch to seal completely. Roll gently into a ball. Repeat.

Prep the air fryer: Line the basket with a parchment liner made for air fryers or cut to size, leaving room for airflow. Lightly spray with oil if your basket tends to stick.

Arrange and flatten: Place 3–5 stuffed dough balls in the basket, leaving space to spread. Gently press each ball to about 3/4-inch thickness for even cooking.

Air fry: Cook at 320°F (160°C) for 7–9 minutes, until edges are set and lightly golden but centers still look soft. Every air fryer is different—check at 7 minutes and add a minute as needed.

Finish and rest: Sprinkle with flaky sea salt if using. Let cookies rest in the basket for 3 minutes to set, then transfer to a rack to cool slightly. The centers will be molten.

Repeat: Cook remaining batches the same way. Enjoy warm for the best gooey center.