Preheat and prep: Heat oven to 400°F (200°C). Lightly oil a 9x13-inch baking dish or similar casserole.

Mix the meatballs: In a large bowl, combine ground beef, Italian sausage, almond flour, Parmesan, eggs, garlic, onion powder, Italian seasoning, red pepper flakes, 1–2 tablespoons chopped parsley or basil, 1 teaspoon salt, and 1/2 teaspoon black pepper. Mix gently with your hands until just combined.

Form the meatballs: Roll the mixture into golf-ball-sized meatballs (about 1.5 inches). You should get around 20–24.

Brown the meatballs (optional but recommended): Heat a large skillet over medium-high heat with a drizzle of olive oil. Brown meatballs in batches for 2–3 minutes per side until lightly seared. Transfer to a plate. They won’t be fully cooked yet.

Layer the bake: Spread 1 cup of marinara on the bottom of the baking dish. Nestle the meatballs in a single layer. Spoon remaining marinara evenly over the top.

Add cheese: Sprinkle shredded mozzarella over the meatballs. Top with a generous handful of grated Parmesan.

Bake: Place the dish on the center rack and bake for 18–22 minutes, until the cheese is melted and bubbling and the meatballs reach an internal temperature of 165°F (74°C).

Broil for color: Turn the broiler to high and broil for 1–2 minutes, watching closely, until the cheese is golden and lightly crisp at the edges.

Rest and garnish: Let the bake rest for 5 minutes to set. Sprinkle with fresh basil or parsley and an extra pinch of Parmesan.

Serve: Spoon into bowls and enjoy as is, or pair with sautéed zucchini noodles, roasted broccoli, or a crisp green salad.