In the bowl of a stand mixer, combine the softened butter and both sugars. Beat on medium speed until light and fluffy, about 5 minutes, pausing to scrape down sides of the bowl as needed.

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.

With mixer speed set to low, gradually add the flour mixture to the wet ingredients. Scrape down the bowl once or twice to ensure everything is well-combined.

Carefully beat in the chopped Toblerone to maintain chunky chocolate pieces.

Scoop dough into two-tablespoon-sized balls. Refrigerate for at least 4 hours or up to 3 days.

When ready to bake, preheat your oven to 350°F (175°C). Let the dough come to room temperature while the oven heats.

Place your dough balls three inches apart on parchment-lined baking sheets.

Bake for about 10 minutes until the edges are golden and the center appears soft.

Immediately after pulling them from the oven, top with an extra piece of Toblerone, gently pressing it in. Let them cool for 2 minutes before transferring to wire racks.