Hello,
Been reading through Yannick Alleno's YAM magazine as I discovered it finally exists in English and a lot of recipes have steps as follows:
Vacuum seal, then cook in a steam oven at 83C for 12 hours.
Almost every time vacuum sealing is involved and then the steam oven.
I don't own a steam oven. How could I get an approximate result? Sous vide?
There is also this -

For that celeriac mixture would I just put the dishes in a bain marie in the oven?