Preheat your oven to 350 degrees Fahrenheit and line two baking sheets with parchment paper.
In a large mixing bowl add the cake mix, eggs, and vegetable oil and mix until a dough forms. Note; the dough will be thick.
Next, take a heaping tablespoon of cookie dough roll it into a ball and slightly press it down onto your prepared baking sheets so it is flatter than a cookie dough ball.
Bake in the oven for7-8 minutes. Then allow the cookies to cool completely before adding the frosting on top.
While the cookies are cooling, make the frosting. In a medium saucepan over medium heat, whisk together the butter, cocoa powder, and milk together until everything is melted.
Then remove from the heat, add the powdered sugar and whisk until smooth.
Next, pour the frosting over the cookies, use a knife as needed to spread the frosting to ensure each cookie is completely covered.
Add the pecan halves to the top of the cookies (if using) before the frosting sets.
Once the frosting has set, serve and enjoy!
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Notes
You can store any leftovers of these sheet cake cookies in an airtight container at room temperature for 3-4 days. For longer storage you can freeze them in your freezer for up to 2 months.