Place a 9-inch (22.5 cm) cast iron skillet in the oven. Preheat the oven to 450F (225C).
While the oven preheats and the skillet heats, blend the milk, water, chickpea flour, and oats in a blender until completely smooth.
Once the oven is finished preheating, blend in the baking powder and any of the optional extras (i.e., salt, vanilla extract, and ground cardamom).
Open the oven and add the oil to the hot skillet (wear oven mitts and be careful pouring to avoid splashing and burning). Close the door for 30 seconds to heat the oil.
Remove the skillet and immediately pour in the Dutch baby batter. Bake in the preheated oven for 2 minutes (set your timer!).
Wearing oven mitts, remove the skillet. Working quickly, swirl the batter up the sides of the pan (about 1 inch/2.5 cm). Use a spatula to smooth more of the batter onto the sides (no need for perfection!).
Return the skillet to the oven and continue baking for 13 to 15 minutes until golden brown and set. The surface will appear dry, but the center will be slightly springy when touched.
Cut into wedges and serve immediately with suggested toppings, as desired.
