Preheat oven to 400° F. Adjust oven rack to the center of the oven.
In a bowl, combine the eggs, milk, vanilla, sugar and salt. Whisk to combine. Add the flour and whisk until mixture is free of lumps. Set aside to rest for 15 minutes.
While the batter is resting, add butter to a 10-inch cast iron skillet and put skillet in preheated oven for several minutes until butter is melted and the pan gets hot. Add apples and Apple Cinnamon Syrup to the pan and return to oven for 5-10 minutes, until the apples are tender.
Add batter to the pan slowly and evenly. Cook 20 -22 minutes until puffed and golden. Cool several minutes. Spoon Sugar Plum Jam over the top and dust with confectioner’s sugar. Slice and serve immediately.