Step 1: Prepare the Pickle-Brined Vegetables (Optional, but Recommended). In a small bowl, combine the dill pickle brine and water. Add half of the frozen mixed vegetables (about 2 cups) to the brine. Let them sit at room temperature while you prepare the other components, or refrigerate for up to a few hours.

Step 2: Cook the Potatoes. Place the cubed potatoes and half of the halved garlic cloves (save the rest for the meat filling) in a large pot with enough water to cover. Bring to a boil over high heat. Reduce the heat to medium-low, cover the pot, and simmer until the potatoes are tender, about 20 minutes.

Step 3: Cook the Ground Beef. While the potatoes are cooking, cook the ground beef in a skillet over medium heat, breaking it up with a spoon as it cooks.

Step 4: Add Flour and Remaining Garlic. Once the beef is cooked through, stir in the flour and the remaining halved garlic cloves.

Step 5: Add Vegetables and Liquids. Stir in the remaining (non-brined) frozen mixed vegetables, the drained pickle-brined vegetables, beef broth, ketchup, salt, and black pepper. Cook, stirring occasionally, until the mixture is thickened, about 5 minutes.

Step 6: Transfer to Casserole Dish. Transfer the beef mixture to an oven-proof casserole dish (9×13-inch).

Step 7: Preheat Oven. Preheat the oven to 375 degrees F (190 degrees C).

Step 8: Drain and Mash Potatoes. Drain the cooked potatoes well. Return them to the pot.

Step 9: Add Remaining Potato Ingredients. Slightly smash the potatoes with a potato masher. Add the sour cream and ¼ cup of the shredded Cheddar cheese. Mash until smooth.

Step 10: Top the Filling. Spread the mashed potatoes evenly over the beef mixture in the casserole dish, starting from the center and working your way out to the edges to form a top layer.

Step 11: Sprinkle with Cheese. Sprinkle the remaining ¼ cup of shredded Cheddar cheese over the mashed potatoes.

Step 12: Bake. Bake in the preheated oven until the cheese is melted and golden brown, 20 to 25 minutes.

Step 13: Cool and Serve. Let the Shepherd’s Pie cool for 15 minutes before serving. This allows the filling to set slightly and makes it easier to serve.

Step 14: Garnish and Enjoy! Garnish with finely chopped pickled red onions (if using) and serve with chilled dill pickle spears on the side.