Preheat the oven to 350°F (175°C).
Grease a 9-inch round cake pan and line the bottom with parchment paper.
Whisk together the flour, baking soda, and salt.
Beat the butter, brown sugar, and granulated sugar until light and fluffy.
Mix in the egg, egg yolk, and vanilla extract.
Gradually add the dry ingredients until just combined.
Fold in the chocolate chips evenly.
Spread the dough evenly into the prepared cake pan.
Bake for 22–27 minutes or until the edges are golden and the center is just set.
Cool completely in the pan before removing.
If desired, prepare the frosting by beating butter, powdered sugar, vanilla, and milk until smooth.
Pipe frosting around the edges and decorate with sprinkles before serving.