Preheat the oven to 350 F, line a 9"x9" pan with parchment paper (for easy removal)
Add flour, baking soda, salt and cornstarch to a medium mixing bowl, whisk until combined.
Add softened butter, brown sugar and sugar to a large mixing bowl or bowl of stand mixer. Beat until light and fluffy. Add the non-dairy milk and vanilla and beat until creamy.
Add the dryer mixture to the wet and mix until combined.
With dampened hands, press half the cookie dough evenly into the lined pan. Bake for 10 minutes.
Sprinkle 1 cup of the chocolate chips evenly over the top. Pour the melted cookie butter evenly over the chocolate chips. Press the remaining pieces of cookie dough evenly over the top, covering as much f the cookie butter as you can.
Top with the remaining 1/2 cup chocolate chips and press in slightly. Sprinkle seat salt lightly on top if desired.
Bake in the oven for 18-22 minutes, until light golden brown. Remove and sprinkle again with sea salt if desired. Cool completely, slice into bars. Enjoy!