Step 1

Preheat the oven to 450°F and have ready a rimmed baking lined with nonstick aluminum foil.

Step 2

Add the breadcrumbs, 2 teaspoons Kosher salt, 1 teaspoon onion powder, 1 teaspoon black pepper, 3/4 teaspoon allspice, 1/2 teaspoon nutmeg, 1/2 teaspoon garlic powder, milk, and egg to a large mixing bowl and use a fork to combine. Add the beef and work in with your hands until the crumb mixture is evenly distributed throughout the meat.

Step 3

Scoop out generous, tablespoon-sized portions of the mixture and roll into a ball with damp hands.

Step 4

Place the meatballs on the baking sheet, leaving a 1" gap between them. Use two baking sheets if necessary not to overcrowd the meatballs. Bake for 15-20 minutes, until the meatballs have browned and fully cooked through. Set aside while you make the sauce.

Step 5

Add the butter to a medium-sized saucepan over medium heat. As soon as the butter has melted, whisk in the flour.

Step 6

Add the chicken broth in one big splash at a time, whisking well after each addition. Once all of the broth has been incorporated, stir in the cream, followed by 3/4 teaspoon Kosher salt, 1/2 teaspoon pepper, 1/2 teaspoon allspice, 1/2 teaspoon nutmeg, 1/2 teaspoon garlic powder, 1/4 teaspoon onion powder, and the Worcestershire sauce.

Step 7

Transfer the meatballs to the slow cooker and pour the sauce on top. Cover and cook on high for 1 1/2 to 2 hours, or on low for 3 to 4 hours.

Step 8

Gently stir in the sour cream just before serving. Serve and enjoy!