Add 1 cup rolled oats to a blender or food processor and pulse 3-4 times to break up the oats, but not grind them to flour.
In a medium bowl, whisk together the blended oats, 1 cup all-purpose flour, ½ teaspoon baking soda, ¼ teaspoon baking powder, and ½ teaspoon salt. Set aside.
In a large bowl, beat ½ cup unsalted butter,½ cup dark or light brown sugar, and ⅓ cup granulated sugar until light and fluffy, about 3-4 minutes. Add 1 large egg, and 1 ½ teaspoon vanilla extract and beat until just combined.
Add the dry ingredients to the wet and mix until combined. Stir in ¾ cup cornflake cereal, ⅓ cup shredded sweetened coconut, and ¾ cup milk chocolate chips by hand.
Cover the bowl and chill in the fridge for 30-45 minutes. About 15 minutes before removing the dough from the fridge, preheat the oven to 350 degrees Fahrenheit and line two baking sheets with parchment paper.
Use a large cookie scoop to scoop roughly 3 tablespoons of dough onto the cookie sheets, leaving 2 inches between them.
Bake for 10-12 minutes, until the edges are just starting to turn golden brown. The centers of the cookies will look quite underbaked, but they will continue to cook as they cool.
Let the cookies cool on the baking sheet for 2 minutes before transferring to a cooling rack to finish cooling.