Pre-heat the oven to 400. Whisk the flour, brown sugar and salt together in a mixing bowl to aerate them. Set the bowl aside. Pour the milk into a microwave safe container and warm it for 20 seconds. Then add it to a large mixing bowl and whisk it together with the eggs, maple syrup and vanilla. Slowly pour the dry ingredients in while you keep whisking until a batter is formed. Fold in the walnuts to finish it.

Take a large cast iron skillet and melt the butter in it over medium high heat. When it is all melted, swirl it around to coat the pan and pour the excess into the batter. Whisk the batter again to incorporate the butter, then pour it into the hot pan. Transfer the pan to the oven and let the dutch baby bake for about 20-25 minutes. It should be puffy and golden.

Take the pan out when it is done and let the dutch baby cool for a couple of minutes. Then slice into wedges and serve immediately! I like to top each wedge with extra chopped walnuts and syrup. Powdered sugar would be great too.