Place milk and cereal in a medium bowl.
Stir well and allow to steep for 20-25 minutes. Strain the mixture through a fine mesh sieve into a small bowl.
Gently press the milk out of the cereal using a spatula or wooden spoon.
Separate 1 cup of the cereal milk for the cake. Save the remainder of the cereal milk for another use.
Preheat oven to 350F. Grease and flour three 6" cake rounds, and line them with parchment. Wrap with EvenBake strips.
In a medium bowl, whisk flour, baking powder, cinnamon, and salt and set aside.
Beat butter until smooth. Add sugar and beat on med-high until pale and fluffy (2-3mins).
Reduce speed and add eggs one at a time, fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and cereal milk, beginning and ending with flour (3 additions of flour and 2 of milk) fully incorporating after each addition. Mix until just combined.
Spread batter evenly into prepared pan and smooth the top with a spatula. Bake for 30-35mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on a wire rack to cool for 10mins then turn out onto the wire rack to cool completely.
Preheat oven to 300F. Line a baking sheet with parchment paper or a silicone baking mat.
In a bowl, whisk together all of the dry ingredients for the crumble.
Add the wet ingredients to the dry ingredients and mix until small clumps form.
Spread the crumble mixture evenly onto the prepared baking sheet.
Bake the crumble for 15 minutes.
Allow the crumble to cool completely before using it on the cake.
Cream Cheese Frosting
Beat butter and cream cheese on med-high speed until pale and smooth, about 2 minutes.
Reduce mixer speed to low. Add sugar 1 cup at a time to butter and cream cheese mixture. Then Add vanilla and a pinch of salt to the frosting mixture.
Increase the mixer speed to high and beat for 2-3 minutes until the frosting is pale and smooth.
Place one layer of the baked cake onto a cake stand or serving plate.
Brush the top of the cake layer with 2-3 Tbsp of cereal milk.
Top with 2/3 cup of frosting, spreading evenly. Sprinkle with crumble or crushed cereal.
Repeat the process with the remaining cake layers, brushing each layer with cereal milk, and adding frosting and crumble.
Once the cake is assembled, frost the outside of the entire cake.
Press crushed Cinnamon Toast Crunch cereal into the outer sides of the frosted cake.
Press crushed Cinnamon Toast Crunch cereal into the outer sides of the frosted cake.