How to Make It
Lightly coat a 13- x 9-inch glass or ceramic baking dish with cooking spray. Preheat broiler to high with oven rack in top third of oven. Finely chop white and light green parts of scallions to equal 1/3 cup. (Discard remaining white and light green parts, or reserve for another use.) Reserve green tops of scallions.
Lightly coat corn with cooking spray; arrange on a rimmed baking sheet lined with aluminum foil. Broil, turning occasionally, until slightly charred on all sides, 15 to 20 minutes. Remove from oven; let stand until cool enough to handle, about 10 minutes. Turn oven temperature to 350°F.
While corn cools, heat oil in a medium nonstick skillet over medium-high. Add garlic and reserved 1/3 cup chopped white and light green scallion pieces; cook, stirring constantly, until fragrant, 1 minute. Transfer to a large bowl.
Cut corn kernels from cobs (about 6 cups); discard cobs. Place 1/4 cup water and 2 cups corn kernels in a blender or food processor; process until coarsely ground, about 15 seconds. Transfer mixture to garlic mixture in bowl; stir in milk, eggs, melted butter, and remaining corn kernels. Stir in flour, cilantro, salt, and pepper. Pour into prepared baking dish.
Bake at 350°F until bubbly, about 40 minutes. Let cool 5 minutes. Slice reserved green scallion tops to equal 1 cup. (Discard remaining scallion tops, or reserve for another use.) Sprinkle corn pudding with sliced scallion tops, Cotija cheese, and chili powder; serve warm with lime wedges.