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.)
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.