Using the recipe from seriouseats.com .
Mix equal mass egg, AP flour, and liquid. I used 6 eggs (242g) and Oatley full fat milk, the recipe is actually 3:1 milk:water for the liquid. And 2g / 1/2t salt (whoops, forgot the salt this time but still pretty tasty). Rest overnight.
Pour 2t oil in each well (I use a muffin tin since that's what I have). Preheat tin with oil in the oven until smoking. Pour about 1/4c batter into each well.
Cook 12-15m. (Below, at about 200F interior temperature / 4 minutes.)
Try using a tray with shallower bowls and you'll get proper bowl-like yorkies. Muffin trays will always make them do this weird thing where they cave in on themselves.
Resist the temptation to open the door when they're cooking, or they collapse.
I've also used a 6" flan tray with great results if you want something you can literally serve the whole meal in!
Not sure what oil you used, but sunflower oil gives them a nice flavour. They need very little oil, common mistake is putting too much in the bottom. I go with no more than 1-2mm depth.
I find letting the batter sit too long has a detrimental effect. I find the sweet spot is 30-60 minutes.
My personal mix is 4 large eggs, 250ml regular cow milk, 200g sifted fine plain flour and a lot of salt. Don't over-mix, it should have good legs on it with < 1 minute of an electric whisk.
I preheat the oil at 220c (420f) until smoking. Then I cook at 160c (320f) for 20 minutes.
Gods I love Yorkshire Puddings. Great work, love to see someone else experimenting with them.
Thanks for all the tips! My family is a big fan of them, so I don't think they'll mind if I run some experiments.
The giant yorkshire pudding bowls made in flan trays are awesome - the bottom end up saturated in gravy and delicious, and it's really fun serving the whole meal inside them. But they do take up a lot of oven space. I'm usually cooking for two, which is fine, as two of the 6" trays will sit happily next to each other. If you're cooking for more this might not work.
I grabbed a 6-bowl tray for hosting friends at Christmas (£12 on Amazon) and it worked really well too! (Not the best picture fo them.)
If you do buy one of those trays be sure to get one with a raised rim around the edge. When you pour in the batter you can then fill them to the brim and not worry about the displaced hot oil getting everywhere.