Heat applesauce in a small saucepan over medium heat until hot but not boiling. Pour applesauce into blender. Add the eggs. Blend until combined; about 5 seconds. Add vanilla, sugar, salt and flour. Blend until evenly mixed. Add two tablespoons of melted butter. Blend another 30 seconds.
Heat oven-proof skillet on medium heat. Pour a tablespoon of melted butter into skillet and swirl it around to coat the bottom and sides of the pan. Immediately pour the batter into the skillet; place in middle rack of oven.
Bake until golden brown around the edges and the pancake is puffed, about 20 minutes.
Brush the last tablespoon of melted butter evenly over pancake. Sift powdered sugar over top, if desired.
Mix together 2 tablespoons flour, 1/4 cup sugar, and 1/2 teaspoon cinnamon in a small bowl. Cut in butter until mixture resembles coarse crumbs. Sprinkle over the Dutch Baby. Serve immediately.