Place the butter, granulated sugar and brown sugar in the bowl of a mixer. Beat for 2-3 minutes or until light and fluffy.
Add the eggs and vanilla extract to the bowl. Beat until thoroughly mixed.
In a medium bowl, mix together the flour, cornstarch, baking soda, baking powder and salt. Add half the dry mixture to the mixing bowl and mix on low speed.
Add the remaining dry ingredients and mix on low speed until just combined. Fold in 1 cup of the M&M's.
Cover the dough and chill in the freezer for 10 minutes.
Take two balls of dough (1 1/2 tablespoons in size). Flatten them between your hands and place an Oreo cookie in the middle.
Repeat the process with the remaining dough and Oreos.
Seal the edges, then shape the cookies into discs where about 75% of the dough is on top of the Oreo and 25% of the dough is on the bottom of the Oreo.
Place the cookies at least 2 inches apart on two sheet pans lined with parchment paper or a silicon baking mat. Freeze for 10-15 minutes or until firm.
Preheat the oven to 350 degrees F.
Bake one sheet of cookies at a time for 10-12 minutes or until edges are lightly browned.
After the cookies come out of the oven, immediately press the remaining 3/4 cup of miniature M&M's over the tops of all the cookies.
Let the cookies rest for 5-7 minutes, then transfer to a cooling rack. Serve when cooled, or store in an airtight container for up to 5 days.