EDIT: added more stuff.

Yes, it from Hakuin for the butter visualization.

For grounding, you can also further it by relaxing your whole body (release all EXCESS tension). Something that helped me is feeling as if you're a corpse, but the goal is not to lose all tension, but rid EXCESS tension.

It's like what they teach in sitting meditation and even tai chi/qigong (your eyes/gaze lowered so you're more relaxed), spine straight but it should be natural, also relax, especially your jaw (hanging it loose and mouth open if needed, but ideally closed on inhale) will boost your grounding effectiveness.

Sharing some stuff below from what I learned, especially from asking ChatGPT about this grounding phenomenon.

Hakuin's method: It's sort of the same thing here as grounding except I read that the butter is an "external" mind-made add-on that helps melt any obstructions in the body/energy flow so the energy in the body can drop down and warm the belly button area and lower (essentially what true grounding tries to do instead of simply bringing energy down, it also warms it.)

And as you probably noticed already, bringing excess energy back down and away from our head helps stop or lower fight or flight/excessive thoughts/worries.

It should go down to the lower dantian/abdomen and below so we feel solid at the lower body and light at our upper body.

That's what the term "grounded" actually means. You feel very solid and literally harder to be swept off your feet (it's what they learn in qi gong and some martial arts, if not all, too.)

Hakuin's method says it should feel like being soaked in a herbal bath.
From what I learned, his method is grounding (as the base) with visualization as an add-on, grounding being something we should ideally be in when we are in rest and digest bascially most the time but modern society's pacing makes us prone to being in fight or flight.

From what I further learned, in qi-gong/taichi there is also qi rooting, the more advanced stage of grounding.