Nachos with Raw Corn Pico de Gallo

Name: Nachos with Raw Corn Pico de Gallo
Ingredients: 1/4 cup finely chopped red onion; 2 cups fresh corn kernels (from 2 to 3 large ears); 1/2 cup fresh cilantro, chopped; 1/3 cup grape tomatoes, quartered; 2 tablespoons sliced pickled jalapeños, chopped, plus 1 tablespoon brine; Juice of 1 large lime; Kosher salt and freshly ground pepper; 1 tablespoon unsalted butter; 1 tablespoon all-purpose flour; 1/4 teaspoon chili powder; 1 1/2 cups whole milk; 4 ounces sharp cheddar cheese, grated; 4 ounces Pepper Jack cheese, grated; Kosher salt; 9 ounces yellow corn tortilla chips