Put oven rack in middle position and preheat oven to 450°F. Melt butter in skillet over moderate heatthen transfer 2 tablespoons to a blender. Add apple wedges to skillet and cook, turning over once, until beginning to soften, 3 to 5 minutes While apple is cooking, add milk, flour, eggs, granulated sugar, vanilla, and salt to butter in blender and blend until smooth. Pour batter over apple and transfer skillet to oven. Bake until pancake is puffed and golden, about 15 minutes. Dust with confectioners sugar and serve immediately. Makes 2 servings. Gourmet