Traveling on a glacier in a two person route team is risky business, because stopping the fall and then trying to build an anchor with the weight of your fallen partner on your harness is a significant challenge.
Studies by the French national mountain guide school have determined that a few bulky brake knots in the rope between a two person team can significantly help with crevasse rescue, as long as there is sufficient snow on the surface.
While a standard figure 8 on a bight loop or butterfly knot is partially effective, the brake knot is even better. It creates a larger diameter, more spherical-shaped knot that offers more friction against the snow.
Here’s the method they recommend to tie the knot. Fortunately, it's a simple modification of the figure 8 on a bight, so it should be easy to learn and remember for pretty much anyone.
Tip - Don't make the loops too large, because this is just wasting rope.
Start with a standard figure 8 on a bight, with a loop of about 1 foot.
Next, tuck the loop around the knot . . .
and finally, pass the loop back through the knot, then snug down each strand to dress it. The final loop created should be just a few inches tall.
The knot tying instructions starts at 6:20 In the video below, hopefully this link should take you right there.