In a large bowl, whisk the oil, vinegar and mustard. Toss with the mushrooms and let marinate 15 minutes. Add the kale, toss, then season with salt and pepper.
Meanwhile, preheat the oven to 425 degrees . With 1 tsp. butter, grease four 2-cup ramekins and place on a rimmed baking sheet.
In a large saucepan, bring 2 cups milk, the corn, scallions and 1 1/4 tsp. salt to a boil over medium-high. Add the cornmeal and cook, whisking constantly, until very thick, about 1 minute; pour into a large bowl. Whisk in 4 tbsp. butter, the egg yolks, 1 cup cheese and the remaining 1/2 cup milk.
In another large bowl, using an electric mixer, beat the egg whites until stiff but not dry. Gently fold into the warm cornmeal mixture in three additions. Divide among the prepared ramekins and sprinkle with the remaining 1/2 cup cheese. Bake until puffed and golden, 16 to 18 minutes. Serve with the salad.