Divide the Nutella evenly between 16 cavities of a silicone sphere tray, using about 1½ teaspoons in each cavity.

Divide the creamy peanut butter evenly between the cavities, spooning about 1½ teaspoons directly over each Nutella layer.

Place the tray flat in the freezer for at least 2 hours, until the centers are completely solid.

Beat the softened butter, brown sugar, and granulated sugar together until light and creamy.

Add the eggs and vanilla extract and mix until combined.

Add the flour, baking soda, salt, and cornstarch. Mix just until a cookie dough forms.

Fold in the semi-sweet chocolate chips and peanut butter chips.

Divide the room-temperature dough into 16 equal portions, approximately 3 ounces or 85 grams each.

Flatten one portion of dough in your palm. Remove one frozen Nutella and peanut butter center from the silicone tray and place it in the middle of the dough.

Wrap the dough completely around the frozen center and pinch the seams tightly closed. Repeat with the remaining dough and frozen centers.

Place the stuffed dough balls on a tray and refrigerate for 30 minutes.

Preheat the oven to 350°F and line the baking sheets with parchment paper.

Arrange the chilled cookies on the prepared baking sheets, leaving at least 2 inches between them.

Bake for 12 to 14 minutes, until the edges are golden.

As soon as the cookies come out of the oven, press four Reese's Peanut Butter Cup pieces firmly into the top of each cookie.

Let the cookies cool on the baking sheets for 5 minutes so the Reese's pieces melt slightly and stick to the tops.

Transfer the cookies to a wire rack and let them cool completely.

Melt the chocolate chips in the microwave in 30 second intervals, stirring between each, until smooth. Drizzle over the cooled cookies and let the chocolate set.