Summarize the following:
Use a spice grinder to grind the toasted sesame seeds into a fine powder. There should be no solid seeds left when done. If you do not have a spice grinder, consider using a coffee grinder or mortal and pestle, instead. In a small bowl, whisk together the ground sesame seeds, dashi, soy sauce, sugar, sake, rice vinegar, and black pepper until the mixture is evenly blended.  For this sauce, you could pulse the ingredients together using a blender instead of whisking by hand, if desired. Doing so can help combine the solid ingredients—the ground sesame seeds, the sugar, and the black pepper—more thoroughly. Note that this is the other common sauce served with shabu shabu, and it, too, can be purchased commercially to save time. This sauce will end up being light brown. Transfer the sauce to a second shallow serving dish.  The bowl needs to be shallow so that you can dip food into the sauce without difficulty. Do not combine the sesame sauce and ponzu sauce. The two must be kept in separate dishes. The sauce can be served without any garnishes, but garnishes can add color and an extra splash of taste. Thinly sliced green onions, a small sprinkle of chopped garlic, and a dash of ground red pepper are good choices for sesame sauce.  Add the garnishes to taste. Keep in mind that they should accent the sauce, not overwhelm it or mask it. Set the sesame sauce aside until you are ready to serve the shabu shabu.

Summary:
Grind the sesame seeds into a powder. Combine the sauce ingredients. Pour into a serving dish. Add the garnishes, if desired.