Preheat oven to 425° F. In a 9x13 pan, add the 4 tablespoons of butter and put it in the oven to warm the pan and melt the butter.
Meanwhile, in a blender combine the eggs, milk, flour, salt and sourdough starter. Blend to combine.
Remove pan from oven and pour in the batter. If you want to try the apple variation, toss the sliced apple to the top and sprinkle on some cinnamon.
Bake at 425° F for about 20 minutes. Serve immediately with a sprinkle of powdered sugar and lemon juice, or with pure maple syrup.
Note: for all you non-sourdough makers, feel free to make this recipe but simply skip the cup of sourdough starter and follow all other instructions/ingredients. If you use all-purpose flour or bread flour it will puff up really high when coming out of the oven. (Whole wheat flour and Kamut flour is a little heavier and doesn’t rise as high.)