Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Add the vanilla extract and egg yolk to the butter-sugar mixture, and mix well until combined.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Fold in the chocolate chips (or your preferred mix-ins) into the dough.
Roll the dough into a large cookie ball, about 2 to 3 inches in diameter, and place it on the prepared baking sheet. Make sure to leave enough space between the dough ball and the edges of the baking sheet.
Bake for 12-15 minutes, or until the edges are golden brown and the center is slightly soft.
Remove from the oven and let the cookie cool on the baking sheet for a few minutes. It will continue to cook slightly on the sheet.
Transfer the cookie to a wire rack to cool completely, or enjoy it warm.
Feel free to adjust the quantities or add additional mix-ins according to your preferences. Enjoy your big and bold cookie!