Design Eat Repeat

0 Preheat oven to 350°F.
18  [adjustable]Place 12 OREOs in a large ziploc bag and use a rolling pin to crush into fine crumbs (or use a food processor). This amount will give you enough for the dough & topping.[/adjustable]
17 Tip before starting! I will note that this is a thicker dough that is easiest to make with a stand mixer. If you only have a handheld mixer, you may just need to use a spatula to help mix the flour in.  
1 In a large bowl, use an electric mixer on medium-high speed to cream softened  [adjustable]unsalted butter (¾ cup, 1 ½ sticks), light brown sugar (¾ cup), and granulated sugar (¾ cup)[/adjustable] for 2 minutes until light and fluffy.
2 [adjustable]Add the eggs (2 large), vanilla extract (2 teaspoons), and light corn syrup (3 tablespoons) and mix on low speed until combined. Scrape down the sides of the bowl so everything can combine. [/adjustable]
3  [adjustable]Add in baking powder (1 teaspoon) and salt (½ teaspoon) and mix  [/adjustable]for another 5-10 seconds until combined.
4  [adjustable]Lastly, add dark cocoa powder (¾ cup), OREO crumbs (¾ cup) and all-purpose flour (2 cups) and mix on medium until combined. [/adjustable]
5 Spray a light-colored metal 9×13 pan with cooking spray, then line pan with parchment paper, leaving a 2 inch overhang on each long side so that you will be able to lift the bars out of the pan.
15 Drop the dough into 1-tablespoon sized chunks into the prepared pan and spread until smooth on top.Tip: This dough is a little sticky, so to help spread, I recommend spraying your hands with cookie spray or use place another piece of parchment paper on top and continue pressing down.
6 Bake bars at 350°F for 16-20 minutes, or until the center no longer looks wet. The center may look a tiny bit underdone but the bars will continue to bake in the hot pan when cooling.Allow to fully cool before decorating.
To Make Chocolate Coating:
8  [adjustable]In a large microwave-safe mixing bowl, beat the softened unsalted butter (½ cup, i.e. 1 stick), vanilla extract (2 teaspoons), and salt (¼ teaspoon)[/adjustable] on medium-high speed for 1 minute until smooth. Turn the mixer to low speed then slowly add the  [adjustable]dark cocoa powder (3 tablespoons) and powdered sugar (1 cup). You may need to stop and scrape down the sides. Add 1 tablespoons of milk. [/adjustable]
20 Microwave for 10 seconds to make glossy & easy to spread.
10 [adjustable]Spread frosting over cooled cookie bars. Top with remaining ¼ cup OREO crumbs and gummy worms. [/adjustable]
16 Allow frosting to firm up before cutting; it's best to refrigerate or freeze for 30 minutes to help set. To get clean slices, fill a tall cup with hot water. In between cuts, dip the knife into the water and use a paper towel to dry it off. When cutting, don't "saw" the bars but rather press straight down and gently lift the knife.