Melt the butter in a 10 inch oven proof skillet while you get the apples ready. Take 2 Tbs butter out and put in a small bowl for the batter. If the butter is melted before the apples are ready, turn the heat down. Put the sliced apples in a bowl, sprinkle with lemon juice and toss, then toss with the sugar and cinnamon. With the heat on medium, add the apples and stir, cooking about 3-4 minutes until the apples are tender.
In a blender, mix the eggs, milk, flour, reserved melted butter and salt. Spread the apples so they're evenly distributed in the pan and turn the heat off. Pour the batter over the apples and put the pan in the oven to bake for 20 minutes.