Gather all your ingredients and preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.

In the bowl of a stand mixer, combine the softened butter, brown sugar, and granulated sugar. Beat on medium speed until light and fluffy for about 5 minutes.

Add the egg and vanilla extract, mixing until fully combined.

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

Reduce the mixer speed to low and gradually add the dry mixture to the wet ingredients, mixing just until combined.

Gently fold in the chopped Toblerone to ensure even distribution.

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

Let the dough come to room temperature for 10-15 minutes. Place dough balls on baking sheets at least 3 inches apart.

Bake in the preheated oven for about 10 minutes. The edges should be golden while the centers remain soft.

Press a small piece of Toblerone into the center of each cookie right after baking. Allow to cool for 2 minutes on the sheet before transferring to wire racks.