The Asian-food fanatic in our house decided to add some brown sugar to his homemade black bean paste one day, and his mom gasped "Eureka!", or something very much like it. Butterscotch mochi now give(s) chocolate chip cookies a run for their virtual money!
The only change to the original recipe is that mung beans have been substituted for the black beans. Because....they're kinda pretty.

Step 1: Sweet Bean "butterscotch" Filling

3 c. dried, split mung beans
2 c. lightly packed brown sugar
1/2 tsp. salt

In a large mixing bowl, soak mung beans in a generous amount of water for several hours or overnight. This step removes most of the....er.....gassy component.

Step 2: Draining and Rinsing

Pour soaked mung beans into a colander, and rinse thoroughly under running water. Transfer beans to a large saucepan or pasta pot, and add fresh water to cover.

Step 3: Cooking the Beans

Place the pot on the burner and turn heat to medium. If you're feeling brave, you can start the cooking process with the heat on high, and turn it down to medium (or medium-low) when steam starts to rise from the pan. Your goal is to bring the beans to a mellow simmer (not a rolling boil!), and to keep them from burning to the bottom of the pan. You will probably need to add hot water from time to time, so that the consistency remains almost soupy. You will thicken the mixture in the final step.

Step 4: Puree the Beans

When the beans are starting to lose their shape (or when they're obviously getting mushy), turn the heat OFF and let the beans cool for a few minutes. If you plan to use a blender to purée the beans, let them cool until they won't cause burns if they splash.
If you plan to use a hand blender (stick blender), just plug it and let 'er rip!

Step 5: Thickening the Bean Paste

When your bean and water mixture resembles smooth pea soup, put it back on a medium-low (or low) heat, and add the brown sugar and salt. Stir slowly to keep the mixture from burning (a silicone spatula is ideal for this), until you can get it to pile up just a little (or a lot, if you want a really firm filling). It's better to have the paste be firmer rather than softer at fridge temperature, because you will be forming it into balls once it is cold.

Step 6: Forming the Filling Into Balls

Lay plastic wrap over a pan (whatever size will fit in your freezer), and form the bean paste into small balls, about one and a quarter inches (or less, if you prefer) in diameter. The scoop in the photo is a one and a half inch cookie scoop, but you can use a spoon, or anything else that works for you. When the balls are complete, cover the pan with another layer of plastic wrap, and place them in the freezer until firm.
This recipe makes about 9 dozen pieces, so you can make a smaller batch, or just keep your extras in the freezer until needed.

Step 7: Mochi Dough

2 c. sweet (mochi) rice flour
1/2 c. wheat starch (corn starch will do as well)
1/4 c. gently packed brown sugar
1/2 tsp. salt
1 Tb. butter (optional)

1-1/4 c. boiling water
Yellow food coloring
1/2 tsp. vanilla

Note: Wheat starch can be found at many Asian markets

Step 8: Preparing the Dough

In a large mixing bowl, stir rice flour and wheat starch together.
In a small saucepan, combine water, sugar, salt, food color, vanilla, and butter. Heat just until the liquid starts to boil, OR microwave ingredients in a Pyrex measuring cup for about 3 minutes, or until steam comes up from the surface.
Dump the liquid mixture directly into the flour and starch mixture, and stir thoroughly with a large spoon.
Allow to sit, covered, for about 30 minutes, or until you can handle the dough comfortably.

Step 9: Dividing and Forming the Dough

Sprinkle your counter (or large cutting board) with rice flour, and turn the dough out onto it. Use enough flour that the dough doesn't stick to your hands. Divide the dough into 3 equal segments, and then divide each segment into 8 balls. This will give you a total of 24.

Step 10: Filling and Shaping the Mochi

Smooth and flatten one piece of dough, and thin the center out slightly with your thumb (this will be the top). Place one frozen filling piece in the center, and pull the sides of the dough up and around, until you can pinch the dough shut. Invert finished mochi onto a flour-dusted pan or plate, and repeat process with remaining dough.Use extra rice flour as needed.
At this point, you can store your mochi in the fridge until you're ready for the final step. If you freeze them, allow them to sit out at room temperature for a few minutes to let the dough warm up a bit.

Step 11: Sesame Sugar

4 c. sesame seeds
4 Tb. granulated sugar

Toast the sesame seeds at 325° for about 15 minutes on a baking pan (with sides -- a large cake pan is ideal)

Step 12: Grinding the Sesame Seeds

When the seeds are cool enough to handle, grind in a food processor or by hand with a mortar and pestle until they look crumbly. Too much grinding will turn them into sesame butter!
Add the sugar and combine. Put about half a cup of the mixture into a small bowl, and set aside.

Step 13: Poaching / Boiling

It is helpful to have a strainer with a shallow bowl shape for this step.
Fill a pasta pot (or other large pot) to a little over three quarters full. Bring to a boil, and drop in up to four mochi. When one starts rising to the surface, scoop it out with the strainer and roll it around a few times to shake the water off. Keep it moving, or it will stick!

Step 14: Coating the Mochi

Roll the mochi off of the strainer into the sesame sugar and flip-roll the ball until it is completely covered. Gently remove the (extremely soft) mochi with your fingers and place on a plate or tray to cool. Repeat the process with the remaining dough and filling. Add more sesame sugar to the bowl as needed.