1-Preheat the oven: to 350°F (177°C) and position the rack to the center.

2-Line a 9×13-inch pan: with parchment paper, allowing overhang for easy removal.

3-In a large bowl, whisk together the flour, cornstarch, baking soda, and salt.

4-In a medium bowl, whisk the melted butter with both brown and granulated sugars until smooth.

5-Add eggs and vanilla extract: to the wet mixture and whisk until combined.

6-Incorporate the wet ingredients: into the dry ingredients with a spoon or spatula until the dough is soft and slick.

7-Fold in the candy-coated chocolates and chocolate chips, noting that some may not stick due to the melted butter.

8-Press the dough evenly: into the prepared pan.

9-Bake: for 26 to 30 minutes, or until the edges are lightly browned, and a toothpick inserted comes out mostly clean with moist crumbs.

10-If the bars brown too quickly before 25 minutes, tent with foil to prevent over-baking.

11-Cool: in the pan on a wire rack for at least one hour.

12-Optionally, press additional candy-coated chocolates and chocolate chips on top while warm.

13-Use the parchment overhang: to lift the bars and slice.