Just a quick idea, as it's Sunday and you might be making your yorkies later for the roast.
Mix your normal yorkshire pudding batter mix.*
Rinse a handful of wild garlic (ramson) leaves under the tap and squeeze the water out. Finely chop and add them to the batter.
This was an experiment as I wasn't at all sure whether the garlic would burn during the cooking process or whether the flavour would work but it was a success. As I love garlic and don't have meat for my roasts I'd put these with anything but I'd imagine them working well with a chicken roast, and maybe lamb.
using a cup. (Video here.) Pretty much all the recipes (including my own) recommend a resting period for the batter mix before cooking. Although not Queen Delia! In fact there's a whole lot of discussion and arguing on the 'perfect' Yorkshire pudding. See here for a little more info.
Anyway, I like to mix mine up a little by adding herbs to the batter, or try a little hard full-flavoured cheese, or wholegrain mustard. I guess horseradish could work for accompanying a beef roast - try it and let me know!