Preheat the oven to 425°F. Line a large baking sheet with parchment paper or lightly coat it with nonstick cooking spray.
Heat a large skillet over medium-high heat. Add the ground sausage and cook for 6-8 minutes, breaking it into crumbles, until browned and fully cooked. Drain any excess grease.
Reduce the heat to low and stir in the softened cream cheese, Parmesan cheese, and black pepper. Mix until the cream cheese is melted and the filling is smooth. Remove from the heat.
Cut each jalapeño in half lengthwise. Remove the seeds and membranes with a spoon for a milder flavor. (Wear gloves if desired to avoid skin irritation.)
Spoon about 1 tablespoon of the sausage mixture into each jalapeño half and arrange them in a single layer on the prepared baking sheet.
Bake for 20-25 minutes, or until the peppers are tender and the filling is hot and lightly browned.
Let the jalapeño poppers cool for 5 minutes before serving.
Notes
Refrigerate leftovers in an airtight container for up to 4 days.
For spicier poppers, leave some of the seeds and membranes in the peppers.
Freshly shredded Parmesan melts better than the shelf-stable grated variety.
These can be assembled up to 24 hours in advance, covered, and refrigerated until ready to bake.