Preheat the oven to 350°F. Line a loaf pan (5-by-9-inch if you're using the hard-boiled eggs, 8½-by-4½-inch if you are not) with parchment paper to cover the bottom and the two long sides, leaving about a 2-inch overhang (the parchment will help you lift the meatloaf out of the pan).

In a large bowl, combine the veal, beef, onions, breadcrumbs, garlic, salt, and uncooked eggs. Mix well with your hands or a wooden spoon until all the ingredients are evenly distributed.

If you are not using the hard-boiled eggs, pile the mixture into the loaf pan and flatten the top evenly. If you are using the hard-boiled eggs, put about one-third of the meat mixture in the pan, arrange the eggs lengthwise in a row down the middle, and pack the rest of the meat mixture around and over the eggs, making sure the eggs are fully covered by the meat and smoothing the top.

Put the loaf pan on a baking sheet and bake the klops until it is deep golden brown on top and the internal temperature is at least 160°F, about 1 hour.

Meanwhile, make the garnish: Heat the oil in a large skillet over medium heat. Add the onions to the pan, season lightly with salt and pepper, and cook, stirring and scraping the pan occasionally, until the onions are nicely caramelized, 25 to 35 minutes. Remove from the heat and keep warm.

To serve, grasp the two sides of the parchment paper and lift the klops out of the loaf pan and onto a serving plate. Slide the parchment out from under the klops and discard. Spread the caramelized onions on top of the klops and slice and serve while still warm.