Melt butter in skillet or 9-inch cake pan. Coat apple slices with butter. Combine 3 tablespoons of the sugar with the cinnamon and sprinkle evenly over apples. Cook over medium heat on stove for 3 to 4 minutes. Cool slightly.
In blender, mix eggs, milk, flour, remaining 3 tablespoons of sugar, and salt. Gently pour mixture over apple slices. Bake until puffed and golden, 15 minutes or a little more. Serve immediately with pure maple syrup.