Make the Panade - In a medium bowl, whisk together eggs and chicken broth. Add breadcrumbs, whisk to combine, and allow to absorb all of the moisture.
Cook the Vegetables - In a microwave-safe bowl, combine olive oil, onion, celery, and garlic. Heat on high power until tender, about 4 minutes, stirring halfway through. Add more time, if needed, in 30-second intervals. Cool the mixture in the refrigerator for 5 minutes.Alternatively, saute vegetables in a medium skillet over medium heat, about 6 to 8 minutes.
Mix the Meatloaf Ingredients - In a large bowl, add the ground beef, Parmesan cheese, breadcrumb mixture, cooled vegetables, tomato paste, parsley, soy sauce, Worcestershire sauce, paprika, salt, pepper, and thyme. Use your hands to gently mix the ingredients until combined, about 1 minute, being careful not to overmix.
Shape the Meatloaf - Fold a double-layer piece of aluminum foil into a 12 by 9-inch sling. Shape the meat into a 9 by 4-inch domed loaf, about 2-inches tall. Place it in the center of the foil sling. Then grab the edges and carefully transfer it to a 6-quart slow cooker.
Make the Glaze - In a small bowl, whisk together maple syrup, tomato paste, apple cider vinegar, Worcestershire sauce, salt, and black pepper.
Add the Glaze - Add 3 tablespoons of the glaze to a bowl. Brush over the top and sides of the meatloaf. Reserve the remaining sauce to use for topping later.
Slow Cook the Meatloaf - Cover and cook until the internal temperature reaches 155 to 160ºF (68 to 71ºC), about 2 1/2 to 3 1/2 hours on low setting.
Rest the Meatloaf - Carefully remove the meatloaf using the sling, draining the juices into the pot. Transfer to a cutting board. Rest for at least 15 minutes before slicing.
To Serve - If desired, warm up the reserved glaze in the microwave until hot. Brush the top of the meatloaf with the glaze or serve on the side. Slice the meatloaf into even-sized pieces. If not serving immediately, transfer to a cleaned slow cooker, cover, and keep on the warm setting for up to 1 hour.
Notes
Breadcrumbs: You can use traditional breadcrumbs, but the texture will be slightly denser.
Storage: Cool completely and store in an airtight container in the refrigerator for up to 5 days. It’s easier to reheat sliced pieces.
Extra sauce: Double the glaze for more sauce to serve on the side.
Broil (Optional): To caramelize the crust, broil the meatloaf on a foil-lined baking sheet. Set the oven rack 6-inches away from the broiler element. Heat the oven to broil on high. Brush the top and sides of the meatloaf with the remaining glaze. Broil until the surface lightly browns, about 5 to 7 minutes. Keep a close eye on the oven as it could burn!