Preheat the oven to 350°F. Line a loaf pan with parchment, leaving the ends hanging over the sides so you can lift the meatloaf out later.

Melt the butter in a skillet over medium heat. Add the chopped apple, onion and garlic and cook, stirring now and then, until the onion is soft and translucent, about 5 to 7 minutes. Take it off the heat and let it cool for about 10 minutes.

Pulse the Ritz crackers in a food processor until they are fine crumbs. Add the cooled apple mixture and pulse a few times, just until it is chopped fine and mixed into the crumbs.

Scrape the apple and cracker mixture into a large bowl. Add the ground beef, egg, Dijon mustard if using, and salt and pepper. Mix with your hands just until everything is combined. Do not overmix.

Press the mixture into the lined loaf pan and smooth the top.

Bake for 45 to 55 minutes, until an instant-read thermometer in the center of the loaf reads 160°F.

Let the meatloaf rest in the pan for 10 minutes, then lift it out and slice.