saute the veggies: Heat the butter in a skillet over medium-high heat. Add the onions and a pinch of salt. Stir as needed and let them soften and turn translucent, about 4-5 minutes. Add the bell peppers and let them cook for 1 minute, remove from heat. Stir in the Italian seasoning, garlic powder, onion powder, and cayenne. Allow the mixture to cool to room temperature before adding to the dip mix.

make the dip: Position a rack in the center of the oven and preheat the oven to 400ºF. Add the cream cheese to a large bowl and whip it using a hand mixer for 30 seconds. You can also do this with a rubber spatula. The cream cheese should still have some resistance to it. Add the mayo, sour cream, and red wine vinegar and mix it together using a rubber spatula. Season with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Stir in the sauteed veggies, roast beef, and 1 1/2 cups of shredded cheese.

bake: Spray a cast iron skillet or a 9x9 baking dish with nonstick cooking spray; add the prepared dip. Flatten out the dip and top with the remaining shredded cheese. Place the dish on a baking sheet to prevent spill over in the oven. Bake the dip for 20-25 minute. You can also pop it under the broiler for the last 1-2 minutes to get the cheese extra bubbly on top! Serve warm with crostini!