Preheat oven to 425°F. Prepare the metal muffin pans by adding enough oil to give a depth of about 3mm, then swirl it around in the pan so it goes up the sides.
Put the oiled muffin pans in the oven on a baking tray that's set at the bottom of the oven for 10 minutes. until the pan is literally smoking hot.
In a medium bowl, add the all-purpose flour, chickpea flour, baking powder, and salt. Then whisk them together until fully combined.
In another bowl, combine the mustard, apple cider vinegar, aquafaba, and water. Whisk them together.
Pour the combined liquids into the dry ingredients and whisk together until smooth and bubbly. Pour into a jug to make pouring quick and easy, then leave to rest for 5 minutes.
Very quickly, but very carefully, remove the muffin pan from the oven, making sure to close the door to keep the heat in. In a long, thin stream, pour the batter into the hot oil in each well of the pan. You need to fill them nearly to the top. The oil will normally rise above the batter, that's what gives you the bowl shape of the puddings.
As soon as the wells are all full, put the pan right back into the oven and shut the door quickly.
Bake the puddings for at least 30 minutes until really golden and crispy and until the insides have dried out to your liking. Do not open the oven door, not even for a quick peek until you are past 25 minutes of cooking.
Remove the puddings from the oven and serve immediately.
Enjoy with family and friends!