Choose a container large enough to hold your food, with plenty of room for the water to circulate. Attach the Sansaire to the side of the container using the clamp and add water until the level is above the minimum fill line but below the maximum fill line. Remember that the water level will rise when you add your food.

Plug in and turn on your immersion circulator, turning the silver temperature ring above the display to 185 degrees. Wait until the target water temperature has been achieved before starting to cook.

Using a vegetable peeler, peel the asparagus from the tip towards the base.

Line up the asparagus on a cutting board, with the bottom of the Ziploc bag as your guide to how long your asparagus should be cut. Using a sharp knife, carefully cut the asparagus so that the lengths are about the same size as the bag to enable the asparagus to snuggly fit into the bag.

Place the asparagus and butter into the Ziploc bag, so that the bottom of the asparagus is flat within the bag. With the top of the Ziploc bag open, carefully submerge the bag into the bottom of the water bath, without allowing any water into the bag itself. The pressure of the water circulating around the outside of the bag will push any air out of the bag and form a seal around the asparagus. Using the side of the water container, carefully seal the bag and leave the asparagus to cook in the water until tender, 15 minutes.

Meanwhile, pan-fry the pancetta until crispy. Reserve.

To Serve: Using tongs, carefully remove the asparagus from the Ziploc bag into a warmed platter. Working one at a time, crack and open the sous vide eggs into a small bowl. Use a slotted spoon to place the egg on top of the asparagus, discarding any unset egg white that remains in the bowl. Top with hollandaise sauce, lemon zest, cayenne pepper and salt, to taste. Serve immediately.