In the bowl of a stand mixer, combine the softened butter, brown sugar, and granulated sugar. Beat on medium speed until light and fluffy, about 5 minutes. Remember to pause to scrape down the sides of the bowl and beater to ensure even mixing.

Beat in the large egg and vanilla extract until fully integrated.

In a separate medium bowl, whisk together the flour, baking soda, and kosher salt.

Reduce the mixer speed to low and gradually add the flour mixture into the creamed butter mixture. Mix until just combined, scraping down the sides of the bowl again.

Gently mix in the chopped Toblerone until it’s evenly distributed throughout the dough.

Scoop the dough into two-tablespoon-sized balls and place them on a baking sheet. Refrigerate the dough for at least 4 hours, or up to 3 days.

Just before baking, preheat your oven to 350°F (175°C). Allow the cookie dough to come to room temperature while the oven heats up.

Line your baking sheets with parchment paper. Place dough balls about 3 inches apart and bake for 10-12 minutes. The edges should be golden while the center still appears soft.

As soon as you take the cookies out of the oven, top each one with an extra piece of Toblerone, gently pressing it into the warm cookie. Let the cookies cool on the baking sheet for 2 minutes before transferring them to wire racks.