Whilst I’ll admit, I didn’t read the post carefully, I’ve used fillet and silverside (close enough to topside) for wellington. The silverside was when a party demanded wellington but on a budget. It was delicious. I used a duck pate for extra fat during cooking and slow roasted the beef for around 45 minutes (before cooling to room temp.) and then wellingtoned it.
Having gone through my own cooking notes (and got myself salivating) I don’t think I’d put myself through the stress of a wellington with topside. It was stressful and whilst delicious, not a wellington as we’d all expect from fillet.
Classic garlic and herb crust?