Wash and dry all produce. Preheat the oven to 400 degrees. Bring a large pot of salted water to a boil. Halve, peel and finely dice the red onion. Mince or grate the garlic. Cut the mozzarella into small cubes. Trim and discard the bottom inch from the broccolini.

Heat a large drizzle of oil in a large pan over medium-high heat. Add half the onion and cook, tossing for 2-3 minutes, until softened. Add the panko, half the thyme, and half the garlic and cook for an additional 1-2 minutes, until fragrant. Season with salt and pepper. Transfer the mixture to a large bowl.

Roast the broccolini: Toss the broccolini on a baking sheet with a drizzle of oil and a pinch of salt and pepper. Place in the oven for about 20 minutes, turning halfway through, until slightly crispy.

Form the meatballs: Thoroughly mix the ground beef into the panko mixture along with a large pinch of salt (we used 1 teaspoon kosher salt) and pepper. Form the mixture into golf ball-sized meatballs. Press 1 cube of mozzarella into the center of each meatball and seal the meat around the cheese. Reserve the extra mozzarella for step 7.

Add the pasta to the boiling water and cook for 9-11 minutes, until al dente. Heat a large drizzle of oil in the same large pan over high heat. Add the meatballs to the pan and sear for 4-5 minutes, rotating to brown on all sides. Remove from the pan and set aside.

Heat a drizzle of oil in the same pan over medium-high heat. Add the remaining onion, thyme, and garlic to the pan. Cook, tossing, for 2-3 minutes, until softened. Add the tomatoes, beef stock concentrate, 2 teaspoons sugar, and 2 cups water to the pan. Bring to a simmer and season with salt and pepper. Return the meatballs to the sauce to finish cooking through.

Finish: Drain the spaghetti and divide between plates. Top with the sauce and meatballs. Roughly chop the broccolini and sprinkle over the plate. Top with any remaining mozzarella and enjoy!