Preheat oven with a large (9-12 inch) cast iron pan on the middle rack to 450F.
Using a blender or a hand mixer, mix together eggs and milk. Add flour, corn starch and salt, and continue mixing until all ingredients are mixed well.
Open the oven and, being very careful - the pan will be very hot, place 2 tablespoons of butter in the preheated pan. Wearing oven mitts, take the pan out of the oven, and swirl to coat the bottom of the pan. Carefully pour the batter into the hot pan, making sure not to splatter batter on the sides of the pan. Return the pan to the oven and bake for 20-25 minutes. The Dutch baby pancake will puff up around the edges and sometimes around the center. Make sure to keep the door closed until it's ready otherwise it may cause the dough to fall and your Dutch baby will look more like a traditional flat pancake.
Meanwhile, prepare all the toppings, such as fried bacon, poached eggs and onions.
Once your savory Dutch baby pancake is done baking, remove the pan from the oven, being very careful as the pan will be very hot. With the help of a thin spatula, slide the pancake onto a large plate. Top with bacon strips, onions, and poached eggs. Sprinkle with freshly ground black pepper. Cut into wedges and serve hot.