Grease and line 3 6-inch cake tins with cooking spray and parchment paper, respectively.
Place a sleeve of graham crackers in a food processor and put it on high till there are no more big chunks
In a medium bowl, whisk the flour, baking powder, cinnamon, salt, and graham cracker crumbs together. Set this dry ingredients’ mixture aside.
Use an electric mixer with a whisk attachment to beat the butter, granulated sugar, oil, vanilla extract and brown sugar together on medium speed until light and fluffy. It takes about 2-3 minutes.
Now add the eggs, one at a time, beating well after adding each. Ensure that you scrape the bottom of the bowl as and when needed to avoid lumps
Alternate adding the dry ingredients and buttermilk to the egg batter in 5 increments such that you begin and end with the dry ingredients.
Beat the mixture on medium speed just until the flour gets fully incorporated
Spread the batter evenly in all the prepared cake tins and bake in an oven preheated to 350°F for 30 minutes until the cake springs back when poked
Remove the cakes from the pans and let them cool completely before proceeding with the frosting