Preheat the oven to 350°F. Line a large baking sheet with parchment paper.
In a large bowl, beat the softened butter or vegan baking stick and the brown sugar until soft and creamy. About 2-3 minutes.
Then add in your egg yolk and vanilla extract and beat on high speed for another minute until fluffy.
Add the flour mixture, and use a rubber spatula to gently mix it together just until there are no remaining streaks of flour. Do not over-mix the dough after the flour is added.
Add the chocolate and stir just until combined.
Bake the cookies for 12 minutes, or until the outsides are golden brown and the insides still look a little gooey.
The cookies are best within three hours of removing from the oven, but you can store them in an airtight container for up to a week.
