Arrange a rack in the middle of the oven and heat to 375℉.
Place the cream cheese and sour cream in a large bowl and stir to combine. Add the jalapeños, cheddar cheese, garlic powder, salt, and pepper and mix until evenly combined. Transfer the dip to a 9-inch cast iron skillet or 2-quart baking dish.
Place the crushed crackers, Parmesan, and butter in a medium bowl and stir until combined. Sprinkle evenly over the dip.
Bake until the dip is heated through and the top is golden-brown, 20 to 25 minutes. Let cool for 5 minutes before serving. Top with extra diced jalapeños and parsley if desired. Serve warm with chips, crudités, or pretzels for dipping.
