Preheat oven to 375 degrees F. and grease a large rectangle baking dish (9″x13″) with cooking spray.
In a mixing bowl, whisk together the flour, baking soda and salt. In a microwave safe bowl, combine the oil and chocolate chips and microwave for 1 minute. Stir until the chocolate melts and is combined with the oil then whisk in the sugar and vanilla extract. Slowly whisk in the eggs, one at a time, until combined. Add the wet ingredients to the dry ingredients and whisk until smooth.
Chocolate Chip Cookie Dough
In a mixing bowl, whisk together the flour, baking soda and salt. Separately combine the oil, sugar, brown sugar, egg and vanilla extract. Fold the wet ingredients into the dry ingredients until the batter is thick then stir in the chocolate chips.
On a lightly floured surface, unfold both sheets of puff pastry and place them side by side. Attach the two sheets together by pressing the ends together then roll out the long combined puff pastry sheet to flatten and smooth out.
Spread the brownie batter all over the surface of the puff pastry then sprinkle the chocolate chip cookie dough on top of the brownie batter. Carefully roll the pastry lengthwise into a log, just like a cinnamon bun. This process is messy so be prepared to lick your fingers.
Using a sharp knife, cut the log into 16 slices, each around 1 1/2 inches thick. Place the buns in the baking dish then bake for 1 hour, until the puff pastry is fully baked.
While the brookie buns are cooling, whisk together the powdered sugar and milk then drizzle the icing all over the top of the buns. You can never have enough icing!