Preheat the oven to 375°F.
Remove the chuck roast from the refrigerator and allow it to come to room temperature. Pat the meat dry thoroughly with paper towels.
Season the roast on all sides with the Good Seasons Italian Dressing & Seasoning Mix. Rub 1 tablespoon of tomato paste evenly over the beef.
Heat a large cast iron skillet over medium-high heat. Add ½ stick of butter and allow it to melt.
Add the chuck roast to the skillet and sear for about 5 minutes per side, until deeply browned.
Push the roast slightly to one side and add the diced onion to the skillet. Cook until translucent, about 2–3 minutes. Season the onions lightly with salt and pepper.
Pour in the beef consommé, scraping up all the browned bits from the bottom of the skillet.
Add 3 tablespoons giardiniera juice, then spoon 1 cup giardiniera around and over the roast.
Place the remaining ½ stick of butter directly on top of the roast.
Cover the cast iron skillet tightly with foil and transfer to the oven.
Roast for about 3 hours, or until the beef is fork-tender and easily pulls apart. Cooking time may vary slightly depending on the size of the roast — you’re looking for fall-apart tenderness.