Add the onions to a large frying pan over medium heat with two tablespoons of butter. Stir to combine. Season with salt and cook about an hour, adjusting the heat as needed, until deeply caramelized and drastically reduced in size. Set aside covered in the fridge until ready to use.
Preheat oven too 350
Melt 3 tablespoons of the butter and mix it with the breadcrumbs.
Prepare 3 mini springform pans with parchment and butter on all sides.
Split the breadcrumbs into the pans evenly. Press down and around the sides to form a crust.
Put the pans onto a larger baking sheet and put it into the oven to cook and solidify as a crust, 20 minutes.
While the crusts bake, make the filling.
Preheat a cast iron skillet or large frying pan to high heat and add some oil. Add in the steak. Season with salt and pepper. Stir and cook until all the steak is browned around the edges and cooked through.
Add the cream cheese, sour cream, milk, provolone, american cheese, eggs, banana peppers, and steak to the food processor. Process until smooth.
pour the cream cheese filling into the mini pans with the crust. Return to the oven to cook for about 30 minutes until cooked through.
Remove from the oven and allow to rest 2 hours before serving. Warm up the caramelized onions. Serve the cakes at room temp with warm caramelized onions on top.