Preheat the oven to 355 °F (180 °C) and lightly grease a medium baking dish, about 9 by 13 inches.

Heat the olive oil in a large skillet over medium heat. Add the chopped onion and garlic and cook, stirring often, until soft and translucent.

Add the ground beef to the skillet, breaking it up with a spoon, and cook until browned and cooked through and most of the liquid has evaporated.

Stir in the tomato paste, tomato puree, and Dijon mustard until the beef is evenly coated and the mixture looks thick and glossy.

Season the beef mixture with sweet paprika, smoked paprika if using, salt, and pepper. Let it simmer over medium low heat for about 5 minutes until slightly thickened. Stir in the diced pickles if using, then remove from the heat.

In a medium bowl, whisk together the heavy cream and eggs until completely smooth. Stir in half of the shredded Cheddar cheese and a small pinch of salt if needed.

Spread the beef mixture evenly in the prepared baking dish, pressing it gently into the corners.

Pour the cream and egg mixture evenly over the beef, tilting the dish slightly so it seeps into all the gaps.

Sprinkle the remaining Cheddar cheese and all of the mozzarella evenly over the top.

Bake for 25 to 30 minutes, until the top is golden brown, the cheese is bubbling, and the center feels set when gently shaken.

Let the casserole rest for 5 to 10 minutes before slicing. Garnish with chopped parsley or chives and serve warm.