Preheat your oven to 400 degrees.
Slice two tablespoons of the butter and lay them in the bottom of a 9x13 baking dish. When the oven comes to temperature, place in the oven for 3-5 minutes until the butter is melted*. Move the dish around a bit so that the melted butter coats the bottom.
*While the butter is melting, whisk the eggs in a large mixing bowl until lightly beaten, Add the flour, milk and salt and whisk until smooth. When the buttered dish comes out of the oven and is coated, pour the batter into the hot dish and place it back into the oven to bake for 20-25 minutes until the pancake is puffed and golden.
When there’s about 10-15 minutes left on the pancake, melt the remaining two tablespoons of butter in a saute pan over medium heat. Add the sliced apples and stir to coat with the butter. Cook uncovered, stirring occasionally for 4-5 minutes to soften the apples. In a small bowl, stir together the cornstarch and water until combined. Add this mixture to the apples along with the brown sugar and cinnamon. Stir until well combined. Cover the pan and reduce the heat to low. Simmer for 3-4 minutes until the apples are tender and the sauce is thickened.
When the pancake is finished baking, remove it from the oven and spoon the apples evenly over the top. Sprinkle with powdered sugar, slice into 8 pieces and serve.