In a medium bowl, combine ½ cup of whole milk with 1 cup of panko breadcrumbs, letting them absorb for about 5 minutes. Once softened, add 1 beaten egg, 2 minced garlic cloves, 1 teaspoon kosher salt, ½ teaspoon black pepper, ½ teaspoon ground nutmeg, ½ teaspoon allspice, ½ pound of ground beef, and ½ pound of ground pork. Mix until fully combined, and then form the mixture into approximately 20 meatballs.

In a large skillet, melt 1 tablespoon of salted butter over medium heat. Add 12 ounces of frozen pierogies and pour in ¼ cup of water, covering the skillet to steam them for about 5 minutes. Afterward, remove the lid and fry the pierogies for an additional 3-4 minutes, or until they are golden and crispy. Once done, set aside on a plate, keeping them warm.

In the same skillet over medium-high heat, add 1 tablespoon of olive oil and place the meatballs, ensuring they are spaced out. Fry for 7-9 minutes, turning occasionally until the meatballs are browned and cooked through.

In the skillet used for the meatballs, add the remaining tablespoon of salted butter and 1 chopped yellow onion. Sauté for 3-4 minutes until the onion is translucent and soft. Gradually sprinkle in 2 tablespoons of all-purpose flour, stirring continuously for about 1-2 minutes to create a roux.

Slowly whisk in 2 cups of beef broth and the remaining ½ cup of whole milk into the roux, stirring until smooth. Add in 1 tablespoon of Worcestershire sauce and 1 tablespoon of Dijon mustard, along with a pinch of salt and pepper to taste. Let the sauce simmer for about 5-7 minutes until it thickens slightly.

Return the cooked meatballs and fried pierogies to the skillet, gently tossing everything together to coat evenly in the creamy sauce. Cook for an additional 2-3 minutes to heat through. Serve warm, garnished with freshly chopped parsley or dill.