Yorkshire Pudding tins.

Seems to be the same reason that if I make 1 chocolate roulade, using half the recipe it is never as good as when I cook 2!!
Seriously though, if your tins don't have a none stick coating, you could try treating the 6 hole tin like you would a none, non-stick frying pan - found instructions - copied below!

To season your non stick pan:

Wash your non stick pan with soapy water.
Once your pan is dry, lightly rub vegetable or canola oil onto the non stick surface.
Heat the oiled frying pan over medium heat on a burner for about 1-2 minutes.
Once the pan cools, wipe any excess oil from the pan with a paper towel and you're good to go!
Afterwards, our non stick surfaces require just a quick sponge out to rid them of residue. However, you can repeat this seasoning process every once in a while as desired.

Me too Shinamae.
Ohhh the shame of it.

Thank you Beth20 I'll give it a try.

I use a non stick muffin tin, they work well, but I wish I'd kept my mother's old tins.

6 hole silicone 'pan'. I put the batter in the cold but lightly greased 'pan' and they rise lovely. They must go into a hot oven though. Problem is, DH has suddenly decided he wants his Yorkshire pudding in a large square and he doesn't want it to be crispy, he wants it stodgy. I can't win!

Don’t worry. Being Yorkshire born doesn’t amount to a hill of beans - I am and my Yorkshires are a travesty. Shameful!☹️

Yorkshire puddings need it hot so yes, I'd season them.
Cover with a nearly invisible layer of oil both sides. Wipe it off till it's barely there. Bake it upside down for an hour then turn it the right way up for an hour. That's what I fid with mine years ago. I think at about 200⁰...
That's probably sufficient.

The salt thing is part of the drying/cleaning of cast iron before the baking if I remember correctly.

To season a pan you need to pre-heat the oven to very hot. Then put oil into the pan and cook it for a while. Then, don't wash it, just wipe it out after use.
I don't know what your pan is made of but there are instructions for different types here.
How to Season a Pan - YouTube
www.youtube.com/watch?v=w1s1wyd48j0
Though, having said that, I cheat with the frozen ones now!

I've tried the 6's in the big oven and they stick. I can't try the 12's in the MW because it won't fit in. I've made Y puds since before I was married and I've been married 61 years so it's not the batter or the method. I wasn't Yorkshire born but almost - by a few miles .
I suppose it must be the tin.
I might try mixing salt with lard and coating the tin before wiping it off. I wish I'd listened to my Gran and taken note

It sounds to me like the combination microwave is probably the problem, not the six-hole tin.
Have you thought of testing this out by using this tin in your other oven?

That said, I agree that new tins need to become seasoned in order to be properly nin-stick, but I have never had any special method for doing this - just don't over-scrub them after use, and it soon happens naturally!

I buy Aunt Bessie’s..?

I don't tend to use Yorkshire pudding in tins. I generally make a large round one in a circular Pyrex dish. It might actually have been the lid of a long gone casserole dish.
I keep the remainder, either freeze it or reheat it later, and eat it with jam or fruit and cream.

I cook my Yorkshire pudding in a 12 hole non stick muffin tin. I put rapeseed oil in the bottom and make sure it's in a200°c oven for 5 mins them put in the batter and cook for 20 mins . I always make sure I make the batter first thing in the morning so it has at least 6 hours in the fridge. And then put in each milk if it's to thick. I freeze them and only need 5 mins in the oven from frozen.

Maybe it’s using a different oven that’s the problem, rather than the tins themselves?
Possibly your ‘big’ oven is hotter?

Make 12 and freeze the uneaten ones.

My Yorkshire pudding tin was my grandma’s. Very black and ancient looking, but they don’t stick! I never wash it either.

Yes, that is of course possible, but the 6 holes I don't use get kind of burnt-looking and horrid.
I should explain, DH and I don't need 12 yorkies, though they'd get eaten (!), and I've got a new combination microwave and the 12 tin doesn't fit. that's the real reason.

Can you not make half the recipe and cook them in the twelve hole tin?