In a jar, combine Frosted Flakes cereal and milk. Allow mixture to steep for at least two hours.

When ready to use, strain the mixture through a fine-mesh sieve, collecting the milk in a medium bowl. Wring the milk out of the cornflakes, but do not force the mushy cornflakes through the sieve. You want to end up with ~2 cups of cereal milk.

In a jar, combine Frosted Flakes cereal and heavy cream. Allow mixture to steep for at least two hours.

When ready to use, strain the mixture through a fine-mesh sieve, collecting the cream in a medium bowl. Wring the cream out of the cornflakes, but do not force the mushy cornflakes through the sieve. You want to end up with ~⅓ cups of cereal cream.

In the bowl of a stand-up mixer fitted with the paddle attachment, add all of the ingredients and beat mixture on medium-high speed until creamy, about 1 minute. Scrape down the sides of the bowl and beat for additional minute.

Dip each ladyfinger in cereal milk and arrange ladyfingers at bottom of baking dish in a single, even layer.

Add half of the mascarpone cream filling on top of the first layer of ladyfingers and smooth it out with an offset spatula.

Dip remaining ladyfingers into the cereal milk and arrange it on top of the mascarpone cream layer. Add remaining mascarpone cream and smooth out the top.

Cover the dish with plastic wrap so it hits the surface of the tiramisu. Transfer to the refrigerator to chill for at least 4 hours, ideally overnight.

When ready to serve, top with crushed Frosted Flakes cereal.