Begin by heating a skillet over medium heat. Add the butter and allow it to melt. Toss in the chopped onion, green bell pepper, and minced mushrooms. Sauté until they become tender, about 5-7 minutes. This step brings out the natural sweetness in the veggies.

In a large bowl, combine the ground beef, sea salt, cracked black pepper, Worcestershire sauce, Dijon mustard, smoked paprika, tomato paste, and panko breadcrumbs. Incorporate the sautéed vegetables and mix everything gently. Adding the eggs helps bind it all together, but don't overmix—gentle is the name of the game here.

Preheat your oven to 350°F (175°C). Transfer the meat mixture to a loaf pan, shaping it into a loaf. This step is key; you want to ensure it holds its shape while baking.

After forming the loaf, create a shallow well along the top of the meatloaf. Tuck the Provolone cheese slices inside and cover it back up with meat. This will keep the cheese deliciously gooey and melty.

Place your loaf pan in the oven and bake for about 60 minutes or until the meatloaf reaches an internal temperature of 160°F (70°C). If the top begins to brown too quickly, cover it lightly with foil.

Once done, remove the meatloaf from the oven. Allow it to rest for 10-15 minutes before slicing. This is the hardest part—waiting! This resting time allows the juices to redistribute.