Add ½ cup water to Instant Pot, and add ground beef, beef base, dried onion, onion powder and black pepper. Cook on Max pressure for 8 minutes or high pressure for 9 minutes, and quick release. Break up ground beef and boil for a minute or two to remove excess water if there is any. Set Instant Pot to “High” slow cook, and add mayonnaise, shredded cheese, and Velveeta. Cook until cheese is melted. Split pan of rolls in half horizontally and top with beef mixture. Add pickles if desired, and bake at 350 for 20 minutes or until warmed through. These can be prepped in advance, and refrigerated. Then you’ll need to bake for about 45 minutes until heated through.