Preheat to 350°F (175°C). Line baking sheets with parchment paper.
In a large bowl, beat softened butter, granulated sugar, and brown sugar until light and fluffy (about 3–5 minutes). Mix in the egg and vanilla extract until fully combined.
In a separate bowl, whisk together flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture. Stir until just combined—avoid overmixing.
Gently fold in chocolate chips and chopped Kinder Bueno bars.
Scoop rounded balls of dough onto baking sheets, spacing about 2 inches apart. Press extra Kinder Bueno pieces on top if desired.
Bake for 10–12 minutes until edges are lightly golden. Centers should look slightly underbaked.
Let cookies cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.