Step 1

Preheat oven to 350°F.

Step 2

Melt the butter in a medium skillet over medium-high heat. Add the chopped onions and cook, stirring occasionally, until the onions have softened. Remove from heat and let cool slightly.

Step 3

In a large bowl, combine the cooked onions, beef, egg, milk, and bread crumbs. Season with salt and pepper to taste. Mix well.

Step 4

Brush a 12-muffin tin (1/2-cup each) with vegetable oil or extra-virgin olive oil. Divide the ground beef mixture between the muffin tin. Lightly pat it into each well.

Step 5

In a separate small bowl, combine the brown sugar, mustard, and ketchup. Set aside.

Step 6

Bake meatloaf muffins for 10 minutes. Remove meatloaf muffins from the oven and top with ketchup mixture. Bake an additional 10-15 minutes or until meat is no longer pink and a meat thermometer reads 160°F.

Step 7

Let stand for 5 minutes before serving.