Weigh 400 g onion, skin on, into a blender jug. Cut it into pieces small enough for the blender.
Add 35 g garlic cloves, pulled off the core with their skins left on, and 700 g water. Blend until smooth.
Strain through a 120-micron filter bag into a clean container.
Taste a small amount neat soon after blending. Note how sharp it is and how long since you blended it.
Notes
For 100 g squash crudo sauce, add 9 g essence to the base after the quieter aromatic liquids, tasting as you go. The allium should fill the middle without covering the main flavor.