Preheat the oven to 350°F (175°C). Grease a standard loaf pan and set aside.

Melt the butter in a skillet over medium heat. Add the chopped onion and green bell pepper. Sauté for 3-4 minutes, or until softened. Remove from heat and let cool slightly.

In a large mixing bowl, combine the ground beef, crushed Ritz crackers, eggs, shredded cheddar cheese, milk, salt, pepper, and the sautéed onion and bell pepper. Mix gently with your hands or a spoon until just combined. Do not overmix.

Transfer the meat mixture to the prepared loaf pan, pressing it down gently to form an even loaf.

In a small bowl, whisk together the ketchup, brown sugar, and yellow mustard to make the glaze. Spread half of the glaze evenly over the top of the meatloaf.

Bake the meatloaf in the preheated oven for 45 minutes.

Remove the meatloaf from the oven and spread the remaining glaze over the top. Return to the oven and bake for an additional 15 minutes, or until the internal temperature reaches 160°F (71°C).

Let the meatloaf rest in the pan for 10 minutes before slicing and serving. Enjoy!