For the meatballs:
3 tablespoons olive oil
2 large cloves garlic, minced or pressed
1 large yellow onion, finely diced
1 teaspoon coarse kosher salt
1 cup matzo meal
2 jumbo eggs
1 cup water
10 large sprigs flat leaf parsley, finely chopped
1/2 teaspoon ground black pepper
1 pound ground lamb
1 pound extra lean (96/4) ground beef
For the egg and lemon sauce:
1/2 cup extra virgin olive oil
1/2 cup lemon juice
1/2 teaspoon coarse kosher salt
4 jumbo egg yolks
1/8 teaspoon ground turmeric (optional, for color)
To make the meatballs: In a large (12-inch) skillet over medium heat, sauté the garlic in the olive oil just until some small bubbles appear around the garlic and it becomes aromatic, about two minutes.
Add the diced onions and salt to the skillet, and sauté until the onions are softened, translucent, and have wilted considerably but not yet begun to brown, about 10 minutes. Turn off the heat and set the mixture aside to cool to room temperature.
In a large bowl, whisk together the matzo meal, eggs, water, parsley, and black pepper to form a paste. Let sit for about 15 minutes.
When the onions and garlic have cooled, add them to the mixing bowl with the matzo meal paste and stir until thoroughly combined.
Add the ground lamb and beef to the mixing bowl. Using your hands, a sturdy spatula or a wooden spoon, gently combine the ground meats with the matzo meal mixture until just combined.
Preheat the oven to 400°F and line two baking sheets with parchment paper or silicone baking mats. Use an ice cream scoop or 1/4-cup measure to portion out the mixture into meatballs, rolling them by hand and placing on the baking sheets, two inches apart.
Bake the meatballs until cooked through and golden brown on top, about 40 minutes.
To make the egg and lemon sauce: In the top pot of a double boiler over medium heat, whisk the olive oil, lemon juice, salt, egg yolks, and turmeric together. Whisk often and vigorously until hot and thickened enough to coat the back of a wooden spoon, about 10 minutes.
Serve immediately, spooning about a tablespoon of sauce onto each meatball.