Grill the jalapenos, turning them occasionally, until charred on all sides, about 10 minutes. Transfer them to a cutting board and let cool for 5 minutes. Keep the grill on high heat.
Using a small paring knife, peel the jalapenos. Scrape out and discard the seeds and veins. Coarsely chop the chiles and transfer them to a medium bowl. Add the butter, garlic, and parsley and mash together. Season the jalapeno butter with salt and pepper, to taste. Put a square piece of plastic wrap on a work surface. Spoon the jalapeno butter onto the center and roll it up into a 1-inch-diameter log. Refrigerate it until firm, at least 30 minutes, or up to 1 week.
Grill the corn on the hot grill or grill pan, turning occasionally, until it is browned in spots and the kernels are tender, about 15 minutes. Transfer the ears to a platter. Top each ear with a pat of the jalapeno butter, sprinkle with queso fresco, and serve.
*Queso fresco is a fresh cheese found at Latin markets. A mild feta could be substituted.