Add cereal to a large mixing bowl. Pour over melted chocolate and toss well to coat. Spread onto a parchment-lined baking sheet. Let set for 10-15 minutes in the fridge. Break into clusters and set aside. 

Preheat the oven to 350°F. Line a large baking sheet with parchment paper.

In a large mixing bowl, use a handheld mixer (or stand mixer with paddle attachment) to cream together the room temp. butter, sugars, and peanut butter until light and fluffy (about 3-4 minutes). On low speed, beat in the milk and vanilla extract.

Add oats, flour, cinnamon, salt, baking soda and powder. Combine on low speed until a soft dough forms. Fold in half of the chocolate cornflakes. 

Use a ~1.5 tbsp cookie scoop to distribute dough onto baking sheet. Slightly press down each mound with the palm of your hand. Top each cookie with remaining chocolate cornflakes. Bake cookies for 11-12 minutes until light brown with crisp edges. Let cookies cool for 10 minutes before transferring to a wire cooling rack.