Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup.
In a spacious mixing bowl, beat the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy.
Stir in the egg and vanilla extract, mixing until everything is smooth and well combined.
In a separate bowl, whisk together the flour, corn starch, baking soda, and salt.
Gradually add the dry ingredient mixture to the wet ingredients. Mix gently until just combined and a soft dough forms. Be careful not to overmix to keep the cookies tender.
Gently fold in the chopped Oreo pieces and Valentine's Day M&M's until evenly distributed throughout the dough.
Using a large cookie scoop (about 1/4 cup or 4 tablespoons), scoop out 10 equal portions of cookie dough and place them onto your prepared baking sheet. For that bakery-fresh look, press a few extra Oreo pieces and M&M's onto the top of each dough ball.
Bake for about 13 minutes. Don't worry if they look a little soft or gooey in the middle – that's ideal! They will continue to set as they cool, ensuring a wonderfully chewy texture.
Let the cookies cool on the baking sheet for 5 minutes before carefully transferring them to a wire rack to cool completely. Enjoy these delightful treats!