• Grease a 9X13X1½ or 2''. Line with parchment paper.
• Melt the butter. Transfer to a large bowl and let it cool ( this is for the cookie)
• In the same saucepan, melt butter. To this add chocolate and oil. Mix until homogeneous.Keep aside. Let it cool.(this is for the brownie)

MAKING THE COOKIE LAYER

• Preheat oven at 160°c
• In a large mixing bowl, whisk flour, baking soda, salt. Keep aside
• In another bowl, use an electric beater and combine, melted butter, and sugars. Add eggs and vanilla extract. blend until well mixed.
• Now slowly fold in the flour mixture, mix until all the flour is just combined. Add in the chocolate chips. Now the cookie dough is ready.
• Now spread the cookie dough in the prepared sheet/tray pan. keep aside

MAKING THE BROWNIE LAYER

• In a medium bowl, mix the flour, cocoa powder, salt, and baking powder. keep aside
• In the large bowl, whisk eggs, sugar, vanilla extract together.
  
• add the cooled chocolate mixture to the eggs and mix well using a spatula or a whisk.Combine until the batter is homogeneous.
• Now add the flour. the batter will be gooey.
• Pour the batter on to the cookie layer, spread well until the cookie layer is covered completely.
• Bake in the middle rack for 20 to 25 mins, until a tooth pick inserted in the center comes out with crumbs.
• let the cookie brownie bar cool completely in the pan before transferring to a wire rack.
• Cut into bars. Serve with a topping of your choice.