Preheat the oven to 375 degrees.
Place the saffron in a small bowl with about 2 tablespoons of hot water and set aside and allow to sit for at least 10–30 minutes. The saffron threads will release a lovely golden color and aromatic floral flavor.
Rinse the cashews a few times in a strainer and drain.
Place the cashews in the sauce pan and cover with 4 cups of water. Bring to boil, then turn the heat down and simmer on low heat with the lid on for about 40–45 minutes. The cashews should be soft and will look smooth on the outside. Pour the cashews through a strainer, discarding the liquid. Place the cashews in the blender cup.
While the cashews are simmering you can roast the garlic bulb. Cut off the top of the bulb so some of the garlic clove tops are exposed. Wrap the garlic bulb loosely in parchment paper and place on a baking pan or sheet pan. Roast in the oven for 35 minutes or until the garlic clove interiors are soft and slightly golden. We don’t want the garlic to get dark for this recipe, just slightly golden and soft. Usually it’s just the papery part that gets too dark, but if the cloves have dark spots, cut and discard that part. Dark garlic will give an unpleasant bitter taste.
When the garlic bulb has cooled enough to handle, squeeze out the indiviual garlic cloves and place in the blender cup with the cashews.
Wrap a paper towel around the blender cup top to prevent the mixture from splattering out. Start blending the cashews and roasted garlic paste with a pulsing action (turn on for a few seconds, turn off, turn on again). Scrape down the sides with a flexible spatula and add 1 or 2 tablespoons of the very hot water and continue blending. It should be a really thick paste and pretty smooth. It will get smoother and thinner in the next step.
Add the lemon juice, the saffron and its golden liquid, cayenne and the salt if using. Blend until very smooth. It will start to have a little sheen too. It should be fairly thick (forms peaks that hold). If too thick, add more of the hot water a little at a time and blending in between until the consistency is super smooth.
It’s now ready to serve. A sprinkle of cayenne looks pretty and adds a little more piquante. Sweet paprika is also a nice finishing touch.
Silky smooth vegan hollandaise can be stored in the refrigerator for up to 4 days. Glass containers are preferable.