1) Prepare a griddle or griddle pan to high heat.
2) Griddle the jalapenos, turning them occasionally, until charred on all sides, about ten minutes. Transfer them to a cutting board and let cool for five minutes. Keep the grill on high heat.
3) Using a small paring knife, peel the jalapenos. Scrape out and discard the seeds and veins. Coarsely chop the chillies 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 2cm diameter log. Refrigerate it until firm, at least 30 minutes, or up to one week.
3) Griddle the corn on the hot griddle or griddle 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.