Filling
In a medium bowl, start by adding the slices of bread, then add the milk and mash everything well until the bread dissolves.
In a large bowl, add the ground beef, the bread we prepared, the medium onion, grated and a whole egg.
Season with the salt, a pinch of black pepper, the chimichurri and mix everything together very well until combined.
Next, take a handful of this meat mixture and shape it into a burger patty, then repeat this process with all the meat mixture.
Transfer everything to a large baking tray lined with non-stick paper.
Now, with a tablespoon greased with vegetable oil, make a hole in the middle of each beef patty and set aside.
After doing that, grate the boiled eggs using the largest holes on the grater and transfer them to a medium bowl.
Season them with a pinch of salt and a pinch of black pepper.
Add the grated parmesan cheese, the mayonnaise, parsley to taste and mix everything together very well until combined.
Add one tablespoon of this mixture we prepared on top of each beef patty.
Take to a preheated oven at 180° C (350° F) and bake for 25 minutes.
Serve.