Add the wet ingredients to the dry and whisk to combine (until no dry flour is showing). Do not over mix or stir the batter until smooth - a few lumps are ok.
Melt 2 tablespoons butter and add to the batter. Chop apples into small bite size pieces and set aside. Heat a cast iron skillet over medium heat and add the remaining 2 tablespoons of butter.
Bake until the pancake is set in the middle and the edges are starting to brown; about 12-15 minutes. Remove skillet from the oven and let cool for a few minutes before serving.