Set the circulator for 85 C / 185°F.

Cut fennel lengthwise, thick slices.

Halve the onion then cut lengthwise into thick slices.

Combine fennel, onion, 1 tsp salt and pepper with the olive oil in a sous-vide pouch and vacuum seal.

Cook for 40 minutes at 85 C / 185°F.

Cut potatoes crosswise into ¼ inch slices.

Add potatoes, water and remaining tsp of salt into a sous-vide pouch and vacuum seal.

Cook for 25 minutes at 85 C / 185°F.

Remove all ingredients from their pouches and blend well in a serving dish.

Serve immediately.