Heat the oven to 425°F. Slice the jalapeños lengthwise, remove the seeds, and position the pepper halves in a baking dish.
Place the ground sausage in a skillet over medium-high heat. Cook while breaking the meat into small pieces until it is evenly browned and completely cooked through. Drain away any excess grease.
Transfer the cooked sausage to a mixing bowl. Add the softened cream cheese and shredded Parmesan, then stir thoroughly until the ingredients form an evenly combined, creamy mixture.
Spoon the sausage-and-cheese mixture into each prepared jalapeño half. Pack the filling securely inside the peppers, allowing it to rise slightly above the edges when needed.
Place the baking dish in the preheated oven and bake for 20–25 minutes, or until the cheese mixture is bubbling and the tops have developed a golden-brown finish.
Let the stuffed jalapeños cool briefly after removing them from the oven. Serve warm with a preferred dipping sauce.