Cheers for taking on a beef wellington! ambitious dish I haven't done. Would love to.
So the idea here is how we can preserve it, right? 48 hours, you are cool (got the pun there?) as long as you keep it less the 40 degrees. You sound like a brit, so if it gets to five Celsius you might worry.
I wouldn't freeze something for a two day difference, just keep it cold.
A beef dish I made today, I'd be confident in it on Wednesday as long as it was in a consistent cold place. For transport I'd say ziploc bag, press out as much air as necessary, and pack it with ice all around.
Beef Wellington is a dish I've always wanted to make, if you have a good recipe I'd love to hear it, best of luck.
sourdough isn't a recipe, it is a process.