While the water is heating up, prepare the sauce. In a large bowl, whisk together the cashew butter, soy sauce, vinegar, sambal, sesame oil, garlic, and fish sauce, if using.
Once the water is boiling, add the udon and cook them for 1 minute, until the noodles have just separated. Drain and quickly add to the bowl with the sauce, tossing to combine. Divide evenly between 2 to 4 serving bowls. Top each bowl with sesame seeds and scallions.
I don’t typically measure ingredients in grams, but that’s how the udon noodles I purchase are weighed out. The brand I often use is Ganko Oyaji.I get frozen udon noodles from the asian market, but I realize not everyone has access to them. You can substitute dry udon noodles, soba, ramen, or really any pasta of your choice. Shoot for 18 ounces, give or take.If you want to add some protein for a more balanced meal, these noodles would taste great with some grilled steak or chicken added in.