Blending
To blend, in the pastry sense, is to work a mass with an immersion blender until completely smooth and homogeneous. The purpose is physical rather than cosmetic: it builds a stable emulsion in which fat is dispersed through the water phase as very fine droplets.
This is how ganache, mirror glaze, crémeux and many mousse bases are made. A well-blended emulsion gives gloss, keeps stably and does not separate.
The cardinal rule is to introduce no air. Keep the blade fully submerged and tilt the container to release bubbles; never lift the blender towards the surface or move it sharply. Bubbles in a glaze become craters on the finished coating, and in a ganache they mean a loose texture that separates sooner.
Work in a tall narrow beaker, where the mass circulates properly and catches less air. If bubbles do appear, let the mixture stand or pass it through a sieve.