Set out the cream cheese to soften. Preheat your oven to 400 degrees F. Line a sheet pan with foil. Grease the foil with cooking spray.
Rinse and dry the jalapeños. Wear food-safe gloves if possible before cutting them. (See notes.) Starting at the pointy ends, slice them in half the long way, cutting through the middle of the stems as well. (Leave the stems attached so they can be used as handles when serving.)
Use a teaspoon to scrape out the membrane and seeds. (If you want your poppers extra hot, leave two or three seeds inside each half. Or, you can save some seeds to stir into the cream cheese filling.) Wash your hands well after handling the jalapeños.
In a small mixing bowl, stir the cream cheese to soften it. Stir in the prosciutto cubes.
Add the Parmesan, paprika and garlic powder to a dinner plate. Stir to combine.
Fill the jalapeño halves with the cream cheese mixture, smoothing the surface.
Press each pepper half, cream cheese side down, into the Parmesan mixture.
Place the jalapeños poppers, cheese side up, on your baking pan. Melt the butter on the stove or in the microwave. (I place my butter in a small, microwave-safe bowl, and heat it, covered, in the microwave.)
Spoon the melted butter onto each jalapeño popper.
Bake for 15 minutes, uncovered, or until the tops are golden brown and the peppers are tender. Store leftovers covered in the refrigerator for up to four days or freeze them in a single layer in a zip-top bag for up to three months for the best quality.
Notes
Be careful not to touch your face or eyes after cutting the jalapeños, because the capsaicin in them will cause a burning sensation. Wear gloves if you have them and wash your hands very well after handling the peppers.If you can't find little cubes of prosciutto at your grocery store, ask the deli worker to slice the prosciutto ¼-inch thick. Then, you can cut it into little cubes at home.