Start by preheating the oven to 400°F. Begin warming your 10" cast iron skillet up on the stovetop over medium heat. If you don't have a cast iron skillet, you can use any frying pan or saucepan to brown the butter, and bake the Dutch Baby in a casserole dish instead.
Blend all of the batter ingredients (reserving the butter and chocolate chips) in a blender, or in a large bowl with a whisk. Set aside.
Once the skillet is nice and warmed, add in the butter. Ideally it will be room temperature and cut into smaller pieces to make it easier to brown evenly. Brown the butter in the hot pan. This should take approximately 8 minutes. You'll know it's ready when it smells nutty and fragrant and the foam begins to subside. For more tips, see the recipe notes above.
As soon as the butter is browned, pour the batter into the skillet. You'll need to do this quickly so the butter doesn't burn!
Sprinkle the chocolate chips into the batter and butter mixture, then place the whole skillet directly into the preheated oven. Bake for 30 minutes, or until the dutch baby is puffy and browned on top.
Once you pull the dutch baby out of the oven the puffy parts will begin to deflate, rather like a soufflé. You can serve the pancake as is, or sprinkle some powdered sugar across the top. For a sweeter pancake, you may serve with maple syrup, but my family finds this breakfast plenty sweet without it.