Brush 4 ears of corn with melted butter and grill over medium-high heat, turning every 2 minutes until all sides have char marks, about 8-10 minutes total. Let cool 3 minutes then cut kernels off the cob into a large bowl.
Heat a small dry skillet over medium heat. Add chili powder and paprika and stir constantly for 1 minute until fragrant and slightly darkened. Remove immediately from heat.
Whisk together mayonnaise, sour cream, toasted spices, lime juice, and salt in a medium bowl until smooth. Fold in warm corn kernels and toss until every kernel is evenly coated.
Divide the corn mixture evenly among 4 cups. Crumble cotija cheese by hand and sprinkle over each cup. Press down lightly so cheese adheres to creamy corn.
Sprinkle finely chopped cilantro and an extra pinch of chili powder over each cup. Serve immediately while corn is warm for best flavor and texture.
