4 ½ cup (540g)  flour
2 tsp baking soda
2 Tbsp (40g) cornstarch
2 tsp kosher salt
1 ½ cup butter, melted
4 cups (400 g) brown sugar
1 ⅓ cup (265 g) white sugar
4 eggs
2 Tbsp vanilla
4 cup chocolate chips, mini eggs, pecans etc

1. Preheat oven to 350F.  Line an 11"X8" baking dish with parchment. 
2. In a bowl, mix flour, baking soda, cornstarch, and salt. Set aside. 
3. In a small pot, melt butter. Add brown and white sugar to melted butter and whisk for 2-3 minutes to dissolve sugar. Add eggs and vanilla. Whisk until thoroughly combined
4. Mix the dry ingredients into the wet. Stir candy into cookie dough just before fully combined. Reserve 1 cup to sprinkle on top of the cookie dough.
5. Bake for 40-45 minutes. Until the sides are set, lightly golden brown and just beginning to puff. Insert a toothpick in the centre and it should come out mostly clean. (Bake closer to 40 minutes if you prefer gooey cookies.  
6. Allow to cool completely before cutting into bars.