Preheat oven to 350°. Grease a 2-qt. baking or gratin dish with the butter. Toss strawberry halves with cornstarch until evenly coated, then arrange berries, cut side down, in bottom of dish and set aside.
In a blender, whirl eggs, milk, flour, granulated sugar, vanilla, and salt 15 seconds. Pour batter over strawberries.
Bake until puffed, golden brown, and set in the center, about 50 minutes. Dust with powdered sugar and serve warm.
Note: Nutritional analysis is per serving.