Divide the gnocchi evenly among the foil sheets, placing a small mound of gnocchi in the center of each sheet.
Spoon the pesto cream sauce evenly over the gnocchi in each packet, making sure each little pile of gnocchi is coated. Use the back of the spoon to nudge the sauce down into the gnocchi so it doesn’t all run off.
Sprinkle the shredded mozzarella evenly over the top of the sauced gnocchi in each packet.
Fold each foil sheet up into a packet: bring the long sides up to meet over the gnocchi, fold them together tightly a few times to seal, then roll up the ends so no sauce can leak out. You want snug, well-sealed packets so the gnocchi can steam and get tender.
Arrange the foil packets in the slow cooker, stacking them gently if needed so they all fit. It’s fine if they overlap; just don’t press them down too firmly.
Cover the slow cooker with the lid and cook on HIGH for 2 to 2 1/2 hours, or on LOW for 4 to 4 1/2 hours, until the gnocchi are tender and the cheese inside is melted and stretchy.
Turn off the slow cooker and carefully use tongs to lift out a test packet. Open it away from your face to avoid the hot steam and check that the gnocchi are soft and the sauce is bubbly and creamy.
When ready to serve, let everyone open their own foil packet at the table. If you like, you can carefully open each packet and slide the contents into bowls, scraping out every bit of the cheesy pesto sauce.
For picky eaters, you can make half the packets with just gnocchi, cream, and mozzarella (skip the pesto in those packets) and label them with a little fold in the foil so you know which is which. If your family likes extra saucy pasta, add another 1/4 to 1/2 cup of cream to the pesto mixture. To lighten things up a bit, you can swap half of the heavy cream for whole milk, though the sauce will be slightly thinner. For a bit more flavor, sprinkle a pinch of salt, black pepper, or Italian seasoning over the gnocchi before sealing the packets. If your crew loves a browned, bubbly top, you can transfer opened packets to a baking sheet and broil for 2 to 3 minutes after slow cooking to toast the cheese. Add-ins like a small handful of frozen peas, baby spinach, or cooked, crumbled Italian sausage can be tucked into individual packets before sealing for family members who like a little something extra. Leftovers reheat best if you open the foil, transfer to a microwave-safe dish, and warm gently with a splash of milk or cream to loosen the sauce.
