Preheat the oven to 400F.
Add the eggs, breadcrumbs, and pureed onion to a very large bowl. Mix well with a fork to combine.
Combine all of the seasonings in a small bowl and mix well.
Add the ground beef to the egg, breadcrumb, and pureed onion mixture. Sprinkle with the seasonings, and mix well with a large wooden spoon.
Once it becomes difficult to mix with a spoon, use clean hands to ensure the meat, seasonings, breadcrumb, eggs, and onion are uniformly combined.
Prepare a full size baking sheet by lining it with parchment paper, or two half size sheets.
Use a medium (#40 or 1.5 Tbsp. size) cookie scoop to perfectly portion the ground beef mixture, and then roll each portion between your hands to form a round meatball. Place the meatball on the prepared baking sheet.
Continue with the rest of the meat mixture, leaving ½" of space around each meatball to ensure even cooking.
Once all of the meatballs have been made, and are placed on the prepared baking sheet(s), place them in the oven.
Bake for 30 minutes, or until an instant read thermometer reads at least 160F. Ensure to check meatballs on the edges, as well as the middle to ensure even cooking. Some may be cooked, while others need to continue to bake.
Once the meatballs have cooked through, remove them from the oven and drain off any excess fat. Remove the meatballs from the baking sheet, and place them on a wire rack to drain. I like to place an extra baking sheet under them to catch the fat. If you don't have a wire rack, you can drain them on paper towel lined plates.